GB/T 15936.6-1996 Information processing text and office systems Office document architecture (ODA) and interchange formats Part 6: Character content architecture
Some standard content:
GB/T 15936.61996
This standard is equivalent to the international standard IS086136:1989 Information processing texts and office systems Office document architecture (ODA) and exchange formats Part 6: Character content architecture". By formulating this national standard, information processing texts and office system files can be easily exchanged. The differences between this standard and ISO86136 are as follows: a) When other standards are cited in the text and appendix, the standard number of my country is used instead of the corresponding international standard number. The corresponding relationship is: GB 1588—1989
GR 2311-1990
GB5261-1985
GB 8565-1988
GB/T 14814-1993
GB/T 15936
GB/T16212—1996
replaces ISO 646; 1983
replaces 1SO 2022:1986
Replaces ISO6429:1983
Replaces IS06937:1983
Replaces 1SO8879:1986
Replaces 150 8613:1989
Replaces 1S0 8824:1990
b) According to the basic provisions for the preparation of national standards, this standard retains the "Foreword of the adopted international standard and adds "Foreword". GB/T 15936 is under the general title of "Information Processing
Text and Office Systems Office Document System Architecture and Interchange Format", which currently includes the following eight parts:
Part 1 (i.e. GB/T15936.1): Introduction and Guidelines; Part 2 (i.e. GB/T15936.2), File Structure; Part 4 (i.e. GB/T15936.4): File Outline; Part 5 (i.e. GB/T15936.5): Office Document Interchange Format (ODIF); Part 6 (i.e. GB/T15936.6) Character Content System Architecture; Part 7 (i.e. GB/T15936.7): Raster Graphics Content System Architecture; Part 8 (i.e. GB/T15936.8): Geometric Graphics Content System Architecture; Part 10 (i.e. GB/T15936.10); Form Specification. Appendix E of this standard is the appendix of the standard.
Appendix A, Appendix B, Appendix C and Appendix D of this standard All of them are appendices of the instructions. This standard was proposed by the Ministry of Electronic Industry of the People's Republic of China. This standard is under the jurisdiction of the Standardization Research Institute of the Ministry of Electronic Industry. The drafting unit of this standard: Standardization Research Institute of the Ministry of Electronic Industry. The main undertakers of this standard: Li Jian, Feng Hui, Huang Weimin. CB/T 15936. 6—1996
ISO Foreword
ISO (International Organization for Standardization) is a world organization composed of various national standardization organizations (member bodies of ISO). The organization formulates international standards through its various technical committees. Every member body interested in a certain profession for which a technical committee has been established has the right to participate in the technical committee. Official and non-official international organizations associated with ISO can also participate in the formulation of international standards. ISO and the International Electrotechnical Commission (IEC) work closely on all aspects of electronic technology standardization. The draft international standards proposed by each technical committee must first be circulated to each member body for voting and approval, and then approved by the ISO Council as international standards. According to ISO working guidelines, international standards require at least 75% approval of the voting members. International Standard IS()8613-6 was prepared by ISO/TC97\Information Processing Systems\Technical Committee. Months ago. ISO8613 consists of seven parts: Part 1: General terms and general principles; Part 2: Document structure; Part 4: Document rotation; Part 5: Office document interchange format (O1)I); Part 6: Character content architecture Part 7: Photographic content architecture: Part 8 + Geometric graphics content architecture. Note: There is currently no Part 3. This International Standard may be supplemented by new parts.
This international standard was developed in parallel with the following standards: FECMA101:1985: Office Document Architecture; -CCITTT.73:1984. File Exchange Protocol for Telematic Services -CCITTT.410 Series of Recommendations: 1988: Open Document Architecture (ODA) and Interchange Formats. This standard contains three appendices:
Appendix A (suggestive appendix): Summary of content architecture classes; - Appendix B (suggestive appendix): Character content architecture classes + - Appendix C (suggestive appendix): Coded representation of control functions; - Appendix D (suggestive appendix): Summary of object identifiers; - Appendix E (normative appendix): ODI represented by SGMI. of character content specific attributes. National Standard of the People's Republic of China
Information processing-Text and office systeusOffice Document Architecture (ODA) and interchange forpat-Part 6: Character content architectures
Inforimation processing-Text and office systeusOffice Document Architecture (ODA) and interchange forpat-Part 6: Character content architectures1 Scope
The purpose of GB/T 15936 is to facilitate the exchange of documents. GB/T 15936.6—1996
idt [so 8613-6:1989
In GB/T15936, files are considered to be items such as memos, letters, invoices, forms and reports that may include images and tabular materials. The content elements used in files may include graphic text lines, geometric elements and raster graphic elements, or may include all of these at the same time.
Note that GB/T15936 is designed to allow expansion to include printing features, colors, leaflets and other content types such as sound. CB/T15936 is applicable to file exchange by data communication or by exchanging storage media. GB/T15936 is the following The exchange of files between two or either of the two dates: allowing presentation as intended by the originator; - allowing processing such as editing and reformatting. The composition of the files in the exchange can have several forms: - a formatted form that allows presentation of the file +
a processable form that allows processing of the file;
- a formatted processable form that allows both presentation and processing. GB/T15936 also provides for the exchange of ODA information structures for processing the files being exchanged. In addition, GB/T15936 also allows the exchange of files containing one or more different types of content, such as character text, images, graphics and commercial audio.
GB/T This part of GB/T 15936
defines character content architectures that can be used with the document architectures specified in GB/T 15936.2: defines the internal structure of content consistent with these character content architectures; defines the positioning and imaging of the presentation in the basic layout objects applicable to these character content architectures; defines the presentation attributes and control functions applicable to these character content architectures; describes a content layout process that, together with the document layout process described in GB/T 15936.2, determines the layout of character content in the basic layout objects and the size of these basic layout objects. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard was published, the versions shown were valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB1988-1989 Information processing seven-bit coded character set for information exchange (idtIS()646:1983) Approved by the State Bureau of Technical Supervision on April 10, 1996 and implemented on December 1, 1996
GR/T 15936.6-1996
Information processing seven-bit eight-bit coded character set code expansion technology (idtISO2022:1986) GB2311-1990
GB5261-1985 Information processing text and symbol forming equipment for supplementary control functions (idtISO6429:1983) GB8565-1988 Information processing text communication coded character set (idt1S)6937:1983) (GB/T14811-1993 Information processing text and office systems: Standard general purpose markup language (SGM1.)（idtIS（）8879：1986)
GB/T16262-1996 Information processing system Uplink and linking system Abstract Syntax Notation One (ASN,J) Specification (idtISO) 8824:1990)
ISO7350;1984 Registration of graphic character subtables for text communication ISO9541511 Information processing fonts and character information exchange Part 5: Font attributes and character modes 3 Definitions
The terms used in this part of GB/T15936 adopt the term definitions given in GB/T15936.1. 4 General
Character content architecture can be divided into two categories: one is a character content architecture used for formatting content, which can display the document content according to the originator's intention (such as printing or display). Formatted content can be used in any basic component; one is a character content architecture used for processable content, allowing the document content to be processed (such as editing or formatting). Processable content can be used in any basic logical component: a character content architecture for formatting processable content that allows the content of a document to be processed and presented as the originator wishes. Formatted processable content can be used in any basic component. 4.2 Content
Basic component content consistent with the character content architecture is a string. The string is formed by concatenating the strings of the basic component content parts.
The content string consists of a composite of graphic characters, control functions, and spacing characters. 4+3 Presentation Attributes
Presentation attributes apply to basic logical and layout components. The information they contain specifies initial conditions related to the layout, imaging, and selection of graphic characters used in the content of these basic components. Some of these conditions can be modified by control functions contained in the content.
Presentation attributes are divided into the following categories:
-Logical presentation attributes that can be associated with processed and formatted processable character content. These attributes are used during the content layout process but are ignored during the content imaging process: - Layout display attributes, which can be associated with formatted and format-processable character content. These attributes are used during the content imaging process. They can be generated by the content layout process or by the process that produces or edits formatted or format-processable content:
- Common display attributes, which can be associated with all types of character content architectures. These attributes can be used in either or both of the content layout and imaging processes. Note: Display attributes can be applied to the content of basic components in one of two ways. They can be directly specified as an object or object description, or they can be specified by the display style associated with the object or object class description. Alternatively, they can be used only in printing using a default value table (see CB/T15936.2).
is used directly in the object or object class description.
4.4 Control functions
CB/T 15936. 6—1996
Control functions with zero or more parameters can specify information related to the layout or imaging of subsequent graphic characters. Control functions can also be used to expand or replace the graphic character set in use. The scope of application of all control functions is limited to the basic components in which they appear.
The classification of control functions is similar to that of presentation attributes: logical control functions, which can manipulate and format the character content that can be manipulated. These control functions play a role in the content layout process and are ignored in the content imaging process! Layout control functions, which can be used to format and format the character content that can be manipulated. These control functions play a role in the content imaging process and are generated by the content layout process. Alternatively, they may be inserted by the process (not described in GB/T 15936) that generates or edits these formatted or formatted processable contents; common control functions that can be used for all types of character content architectures. These control functions can function in either or both of the content layout and imaging processes. In addition, the formatted processable contents may contain control functions called qualifiers. These qualifiers are used to indicate one or more graphic characters and/or control functions that have been inserted by the content layout process (see Chapter 12). The qualifiers function in the content imaging process. The qualifiers function in the internal layout process by removing them and the character sequences they define. 4.5 Graphic characters
The set of graphic characters used in the content of a basic component and their coded representation are defined by the presentation attributes and code extension control functions (see Clauses 10 and 11.1.17).
Any: "A nest of one or more graphic characters may be used in the content of a basic component, subject to certain restrictions related to the particular content architecture used, and to appropriate indication and invocation according to CB2311. Any non-progressive character contained in the graphic character set may not be used alone, but only in combination with progression characters. 4.6 Spacing characters
The character "space (SP)" may be treated either as a logical control function or as a graphic character. As a graphic character it has a graphic representation in which no graphic symbol appears. As a control function it indicates a potential line break (see 12.2.1.3.2). Note that NLSP (non-breaking space) and simplified space characters with a lower sense, such as "mathematical space", "ciT weak space" and "cn space", are regarded as graphic characters, that is, they are not regarded as line breaks.
4.7 Internal code
The coding representation of content information in the content part is consistent with the rules specified in GB2311. The coding representation of control functions is defined by GB5261 and included in Appendix C. 4.8 Internal structure
4.8.1 Formatted content
Formatted content means that all necessary information related to the layout and imaging of these contents has been prepared. The content is specified. This form of content is intended to be imaged as specified and is not subject to modification or reformatting during editing. Basic component content consistent with the formatted character content system architecture consists of one or more lines of characters. Each pair of adjacent lines is separated by a hard line terminator. The last line (or only line) may or may not be terminated by a hard line terminator: the end of the basic component content implicitly terminates the last line.
4.8.2 Processable content
Processable content is content that has been technically laid out. This form of content is suitable for modification by editing processing. Method: Editing processing is implementation-dependent and is not covered in GB/T 15936. In order to image the content in this form, the content needs to be processed for content layout (see Chapter 12), and the processable content is converted into formatted content (see 4.8.1) or formatted processed content (see 4.8.3). Some logical display attributes and control functions have been defined to cooperate with the processing (encoding or layout processing) of the processable content (see Chapter 7 GB/T15936.6-1996
and Chapter 1). In addition, the character "spacing" can be used as both a morphological character and a control function to indicate where line breaks will occur when the content is laid out. The basic component content consistent with the processable character content architecture includes one or more character sequences. Each pair of adjacent character sequences is separated by a hard line terminator control function. The last (or only one) character sequence may or may not be terminated by a hard line terminator. If the hard line terminator is omitted at the end of the content of a basic logical component and there is another basic logical component connected to it (see GB/T 15936.2), the last character sequence will be connected to the content of the next basic logical component. In all other cases, the end of the content of a basic logical component implicitly reveals the last character sequence. The division of character sequences represents the internal structure of the processable content of the basic logical component. Each character sequence is nameless, with neither a name nor an identifier associated with it, and there is no relationship between character sequences except the sequence itself. 4.8.3 Formatted processable content
Formatted processable content is a content constructed with formatted content and processable content as subsets. In addition to the additional control functions and graphic characters that may have been added by the content layout processing surface,Its structure is identical to that of processable content. It is also identical to that of formatted content, except that it may contain logical control functions and qualifiers. Thus, formatted processable content may be converted to processable content by removing (or ignoring) all control functions, all qualifiers, and all control functions and characters that appear within those qualifiers. Alternatively, formatted processable content may be converted to formatted content by removing (or ignoring) all logical control functions and qualifiers but retaining the control functions and characters within the qualifiers. Note: The conversion of formatted processable content to processable content is a reversible process (provided that the corresponding layout constraints also apply to content layout), but the conversion from formatted processable content to formatted content is not. The formatted form of the basic component consistent with the structure of the formatted processable content consists of one or more lines of characters, each pair of adjacent lines separated by a hard line terminator or a soft line terminator, and the last line (or any line) may or may not be terminated by a hard line terminator. The end of the basic layout component content also implies the end of the last line. The processable form of a basic component consistent with the formatting of the processable character content architecture contains one or more character sequences. Each pair of adjacent character sequences is separated by a hard line terminator. The last (or only) character sequence may or may not be preceded by a hard line terminator. If the hard line terminator is omitted at the end of the basic logical component content and there is another basic logical component linked to it (see GB/T 15936.2), the last character sequence will be connected to the content of the next basic logical component. In all other cases, the end of the basic logical component content implies the completion of the last character sequence. The soft line terminator is used as a separator between lines within the character sequence. The division of character sequences represents the internal structure of the content of the basic logical component. Each character sequence is nameless, with neither a name nor an identifier associated with it. There is no relationship between character sequences except the sequence itself.
5 Character positioning
This clause specifies the positioning method of characters within the basic layout object. This chapter provides the necessary conditions for the positioning of characters belonging to different fonts within the same basic layout object. 5.1 Basic overview 5.1.1 Character fonts In the context of this part of GB/T 15936, the term "graphic character" is an abstract concept; the term refers to a "member" of a set of graphic symbols used to represent information. A "character image" represents the presentation of a graphic character on a display medium. A font is a set of character images that usually have a common design and size. A font attribute set is associated with a complete set of fonts, while a character attribute set is associated with each individual character. These attributes are specified by ISO 9541-5. GB/T15936.6—1996
Font attributes are primarily used to indicate to the receiver the type of font used by the originator of the error, and when no specific font is available, font and character attributes become a guide for the receiver to find a suitable replacement font among other existing fonts. Further information on specifying and calling different fonts in basic objects is given in Chapter 6. 5.12 Direction
In the context of this part of GB/T15936, all directions are expressed by the angle (in units) rotated counterclockwise from a specific reference direction (an example is given in Figure 1). Ning character direction refers to the direction of advancement of consecutive character images within a line box (defined in 5.1.7) and is expressed in the direction relative to the horizontal direction of the layout object (see Figure 4). Line advancement refers to the direction of advancement of consecutive line boxes within the basic layout object and is expressed in the direction relative to the character direction (Figure 11)
Character orientation refers to the character baseline related to the character direction (defined in 5-1.3 The direction of the character direction, line advance and character orientation can only be defined as a basic component. Consider the direction
Rotation angle
Direction=90°
Example of direction in Figure 1
5.1.3 Character image model
The positioning point refers to the reference point related to the character image (see Figure 2). It is used to position the character image within a line box. The transition point also refers to the reference point related to the character image (see Figure 2). It is used to position the next character image. The character baseline is an imaginary line that passes through the character image and is used to define the character orientation. When the character image is in the front view orientation, the character baseline is a horizontal straight line (see Figure 3).
For each character orientation to be used, a positioning point and a transition point must be defined (see Figure 3); that is, the "writing mode" corresponding to the required character orientation is defined in the font description, or the backoff is defined in the file application wheel. Out of bounds refers to the part of the character image that exceeds the positioning point and the transition point (see Figure 2). Out of bounds
Positioning point
Figure 2 Illustration of out of bounds
Transition point
5.1.4 Character spacing
GB/T15936.6—1996
Character direction
Ningfulian-0
Character direction
Character orientation = 180°|| tt||PP Fixed point
EP Transition point
Character base
Character baseline
Character path
Character baseline
Figure 3 Reference points for character image positioning
Character base
Character orientation=
Character path
Character orientation 270
The concept of character spacing only applies to fonts with fixed spacing selected. Character spacing (together with the gap between characters) is used to determine the distance between character images within a line spacing, as specified in 5.2.1. When the gap between characters is zero, the character spacing is equal to the positioning of consecutive character images. The distance between points. The character spacing is independent of the distance between the anchor point and the transition point of the character image. 5.1.5 Action position
The action position is an abstract concept in imaging devices such as cursors. It is used to define control functions in the case of assuming a sequential method of processing character strings (see Chapter 11). The action position indicates a point within the fixed area of the basic layout object at which the operation specified by the next character (graphic character or control function) will be performed.
If the next character is a graphic character, its character image will be positioned at the anchor point at the action position, and the action position will advance in the direction of the character's movement. The value of the spacing is specified by 5.2.1. If the next character is a control function, it will cause the action position to move to another point within the positioning area.
5. 1. 6 Positioning area
The positioning area is a rectangular area, wholly contained within a basic layout object, within which the anchor point and the transition point are positioned (see Figure 4). The out-of-bounds of the character image is allowed to extend beyond the positioning area, but it is not allowed to exceed the edge of the basic layout object. The two edges of the positioning area are called the starting edge and the ending edge (see Figure 4). The definition of the starting edge and the ending edge is determined in such a way that the direction from the starting edge to the ending edge is the same as the direction of the character movement. The other two edges of the positioning area are called the upper edge and the lower edge. The definition of the upper edge and the lower edge is determined in such a way that the direction from the upper edge to the lower edge is the same as the direction of the line movement. The starting and ending edges are respectively indented by a distance from the corresponding edge of the basic layout object, and this distance is called the out-of-bounds displacement (see Figure 4). The out-of-bounds displacement is determined by the font of the character to be positioned in the positioning area. Its value is selected so that when a sequence of multiple character images is positioned in a basic layout object, any character image and its out-of-bounds part will not exceed the edge of the basic layout object. 5. 1.7 Line box
GB/T 15936.6-1996
In the positioning area, a sequence of character images is positioned in an area called a line box (see Figure 11). Each line is a rectangular area extending from the starting edge to the ending edge of the positioning area. Each line box contains: a reference point called the line origin position (see Figure 4). This point is used to position the line box within the basic layout object. It also serves as the action position of the first graphic character or control function of each line. Each line box contains an imaginary line called a reference line (see Figure 4). The reference line passes through the line origin position in the direction of the character's movement. It extends from the starting edge to the ending edge in the line box and is used for the alignment of the character images. The length of the line box is equal to the distance from the starting edge to the ending edge: the width (or height) of the line box is equal to the sum of the forward extension and reverse extension of the line box (see Figure 4). The reverse extension of a line box is the distance from the reference line in the opposite direction of the line to the edge of the line box. The forward extension of a line box is the distance from the reference line in the direction of the line to the edge of the line box. The values of the forward and reverse extensions depend on the maximum extension of the character typeface used in the line box (measured perpendicular to the reference line). In determining the forward and reverse extensions, the values of all displacements of the character image perpendicular to the character direction are taken into account, such as subscripts, superscripts and parallel annotations. NOTE: As an example, take a typeface with a character direction of 0° and 270° in the direction of line progression. When a single typeface is used in a line box, its forward and reverse extensions are equal to its maximum rightward extension and maximum leftward extension respectively, as specified in ISO 9541-5. 5.2 Positioning of character images in a line box
Continuous character images are positioned in a line box in the direction of the character direction. Except for certain characters imaged as subscripts, superscripts or parallel annotations, the positioning points of the character images are aligned with the reference line. Several factors affect the positioning of character images along the reference line: - Spacing between characters:
--alignment;
tabulation;
character sorting;
parallel annotation:
subscript/superscript;
-tight spacing;
-first line displacement;
itemization.
Layout object
Positioning area
Non-compare
5.2.1 Character spacing
Line origin position
Start edge
Out of bounds displacement
Upper edge
Character direction
Inner box
Reference line
Tail edge
Lower edge
Out of bounds displacement
Figure 4 Illustration of the concept of character positioning
The spacing between characters is an additional amount of the distance between the positioning points of adjacent character images along the direction of the character direction (see 5.1.4). Negative values indicate a reduction in the spacing between adjacent character images. Next:
GB/T15936.6—1996
The distance between the anchor points of adjacent character images can be either a quantitative or a variable, depending on the font. Specifically, for a font with fixed spacing, the distance between the anchor points of adjacent character images is independent of the character and is the sum of the character spacing (specified by the display attributes and control functions) and the gap between characters (see Figure 5). For a font with only variable spacing, the distance between the anchor points of adjacent character images is related to the character, that is, it is usually related to the distance between the anchor point and the transfer point of the character, and is the sum of the net transfer amount of the character (determined by the font) and the character spacing (see Figure 6). The degree of spacing, i.e. the width of the SP character graphic, can be determined as follows: if an SP character precedes the first graphic character in a line and is followed by a soft line terminator, or precedes a soft line terminator and is followed by the last graphic character in the line, then the width of the SP character is zero. In fixed-pitch fonts, its default width is equal to the inter-character spacing; in variable-pitch fonts, its width is implicitly defined by the font. For all fonts, its width can be specified by the control function. Character stopwww.bzxz.net
The space between Ning characters
The space between Ning He and Ning He
The space between Ning characters
Figure 5 The distance of fixed-pitch fonts
The distance between the river of characters
The net transfer disk
Figure 6 The distance of variable-pitch fonts
5.2.2 Alignment
The character image is positioned in the line box as follows according to the alignment attributes: Start alignment: place the positioning point of the first character image at the origin of the line; End alignment: place the transfer point of the last character at the end edge of the positioning area! Center the reference line: make the distance from the line origin to the first character image positioning point approximately equal to the distance from the last character image transfer point to the end edge of the positioning area; Align the lines: by appropriately setting the width of the spacer characters and/or the size of the inter-character gap, make the first character image positioning point GB/T15936.6—1996
at the line origin, and make the last character image transfer point overlap with the end edge of the positioning area. 5.2.3 Tabulation
The position of the character image on the reference line can be controlled by a series of tab stops. Each tab stop specifies a point on the reference line relative to the start edge of the positioning area.
A character image string can be placed at each tab stop by the control function in the text. This string can be aligned at the beginning, end, center or around one or more specific characters in the string as follows (see figure): Start alignment: the first character image in the string is positioned at the tab stop + End alignment: the last character image in the string is positioned at the tab stop; Center: the center is placed so that the distance from the first character image position and the last character image position to the tab stop is approximately equal
Around alignment: the first character image in a specific set of characters that appear first in the string is positioned at the tab stop. If the specific set of characters does not appear in the text associated with the tab stop, the default alignment is the end alignment as specified above.
Tabulation stop
(starting pair abandoned
aligned
5-2.4 Character sorting
aligned
(end aligned
ceritred
Figure 7 Tabulation
(surrounding aligned
124156
125476
32,465
In a basic object content, the order of exchange is always the same as that of the In the case of some languages, such as Arabic and Hebrew, where alphabetic text is read from right to left and numeric text is read from left to right, the exchange stream must indicate the change of presentation direction appropriately. This is necessary because the control functions in the character content architecture operate sequentially according to their position in the character stream.
When a string with reverse presentation direction is sandwiched between text with normal presentation direction, the string with reverse presentation direction is The last character image of the character is positioned adjacent to the last character image in the previous string of characters with normal appearance direction (see Figure 8).
Note: In Figure 8, the use of the terms "first" and "last" is related to the order of exchange, while the terms "normal" and "opposite" are related to the direction of the character direction. 5.2.5 Parallel annotation
Two consecutive character strings can be defined so that the first string is used to indicate the development and interpretation of the first. It is intended to be used for Japanese, in the form of kana characters to provide pronunciation and interpretation information for one or more Japanese kanji characters (Ruby). In formatted text, for the case where the character image orientation is vertical or parallel to the character direction, the kana characters are centered above or to the right of the kanji characters respectively (see Figure 9).
When the kana characters are positioned outside the positioning area, it is appropriate to position the kana strings in such a way that they are aligned at the beginning or end with the edge of the available area. GB/F 15936.61996
nterchangeorder
■A type of control function in the display direction
P/D=display direction
HGF123EDCBA
Word derivative left
5.2.6 Subscript/Superscript
Generally the last character of P/D
The last character of P/0
The first character of P/D
The first character of the next general display direction Figure 8 Character Order
The appearance of subscripts allows the action position to move from the reference line in the direction of line advancement. The appearance of superscripts allows the action position to move from the reference line in the opposite direction of line advancement. Within a line box, all combinations of subscript/superscript appearances should result in the action position returning to the reference line before the hard or soft line terminator appears.
5.2.7 Double word kerning
Double word kerning allows the action position defined by the previous character to move. Its distance and direction are determined by the character being imaged and the previous character.
In the case of fixed-pitch fonts, double word kerning is omitted. In the case of variable spacing fonts, the distance between the transition point of one character image and the anchor point of the next character image is modified by the tightness information specified by the character attributes of the font. 5.2.8 First Line Shift
The first line shift can be used to make the character image of the first line of a basic component start at a position different from the line origin position. The shift can be in the same direction as the character movement (producing a first line indent) or in the opposite direction of the character movement (producing an overhang), as shown in Figure 10. 5.2.9 Itemization
Itemization is used to make the item identifier image of the first line of a basic component not directly constrained by the line origin position and the first line shift (see Figure 10). The
item identifier is a character string that is prepended to and separated from the rest of the first line of a basic component. The start and end shifts are undefined relative to the line origin position. These two shifts determine the anchor point of the item identifier and the spacing between the item identifier and the line origin position.
The item identifier can be positioned as follows according to the item identifier alignment attribute: - Start alignment: the positioning point of the first character image of the item identifier is placed at the start offset! - End alignment: the transition point of the last character image of the item identifier is placed at the end offset.
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