11.2 The importance of bidirectional text

Some international formatting requirements must accommodate mixing text of different writing directions.

  • The presentation of right-to-left scripts (e.g. Hebrew, Arabic, Thaana, and Syriac) may be embedded into the presentation of left-to-right scripts.

  • The stylesheet may be mixing its boilerplate text with authored content of either possible direction from many different sources to produce the combined result.

  • The formatter is responsible for placement and interpretation of glyphs on the page based on the character code points in the XSL-FO instance.

  • The stylesheet writer is responsible for protecting text, where possible, from being influenced in the XSL-FO instance being formatted.

Three aspects of writing direction influence the presentation of information in a line.

  • A line has an inline-progression direction determined by the writing direction of the closest ancestral reference area.

    • Information is flowed into lines in the inline-progression direction, independent of the visual order of the characters in the information.

  • A group of adjacent characters may have semantic affinity and would thus be required to be flowed into the lines in groups.

    • Groups are ordered in the inline-progression direction.

    • E.g., in a right-to-left progression direction there may be groups of left-to-right characters.

      • The groups are rendered right-to-left on the line, but the characters in each group are rendered left-to-right.

      • Without grouping, adjacent strings of the same direction would be rendered as a whole, losing the semantic affinity in the characters.

    • E.g., boilerplate information from the stylesheet is often semantically distinct from source file information, needing insulation from undue influence from the content.

  • Characters from different scripts have inherent writing directions that may differ from the inline-progression direction.

    • Usually it is necessary to respect the character direction while accommodating the inline-progression direction (this is the responsibility of the formatter).

    • It may be necessary to override the inherent direction for a special effect.

    • Many characters are not associated with any language and are influenced by their proximity to characters from different scripts.

  • Stylesheet writers can specify the progression direction of the information, the grouping of characters, and the respect or override of the inherent Unicode direction in characters.

Definitive XSL-FO
Definitive XSL-FO
ISBN: 0131403745
EAN: 2147483647
Year: 2002
Pages: 99
Authors: G. Ken Holman

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