I18n checklist: text direction

[fsteeg]

This is a self-review checklist based on the Internationalization Best Practices for Spec Developers.

(I've skipped what seemed formatting and markup related here.)

See also issue #52, #125 and notes at https://etherpad.lobid.org/p/reconciliation-i18n.

Basic requirements

1. It must be possible to indicate base direction for each individual paragraph-level item of natural language text that will be read by someone. more
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2. It must be possible to indicate base direction changes for embedded runs of inline bidirectional text for all localizable text. more
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Background information

1. Do not assume that direction can be determined from language information. more
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Base direction values

1. Values for the default base direction should include left-to-right, right-to-left, and auto. more
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Handling direction in markup

1. The spec should indicate how to define a default base direction for the resource as a whole, ie. set the overall base direction. more
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2. The default base direction, in the absence of other information, should be LTR. more
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3. The content author must be able to indicate parts of the text where the base direction changes. At the block level, this should be achieved using attributes or metadata, and should not rely on Unicode control characters. more
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4. It must be possible to also set the direction for content fragments to auto. This means that the base direction will be determined by examining the content itself. more
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5. If the overall base direction is set to auto for plain text, the direction of content paragraphs should be determined on a paragraph by paragraph basis. more
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Handling base direction for strings

1. Provide metadata constructs that can be used to indicate the base direction of any natural language string. more
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2. Specify that consumers of strings should use heuristics, preferably based on the Unicode Standard first-strong algorithm, to detect the base direction of a string except where metadata is provided. more
   Doesn't this conflict with the point above: The default base direction, in the absence of other information, should be LTR.
3. Where possible, define a field to indicate the default direction for all strings in a given resource or document. more
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4. Do NOT assume that a creating a document-level default without the ability to change direction for any string is sufficient. more
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5. If metadata is not available due to legacy implementations and cannot otherwise be provided, specifications MAY allow a base direction to be interpolated from available language metadata. more
   Doesn't this conflict with the point above: The default base direction, in the absence of other information, should be LTR.
6. Specifications MUST NOT require the production or use of paired bidi controls. more
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Setting base direction for inline or substring text

1. It must be possible to indicate spans of inline text where the base direction changes. If markup is available, this is the preferred method. Otherwise your specification must require that Unicode control characters are recognized by the receiving application, and correctly implemented. more
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2. It must be possible to also set the direction for a span of inline text to auto, which means that the base direction will be determined by examining the content itself. A typical approach here would be to set the direction based on the first strong directional character outside of any markup. more
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3. If users use Unicode bidirectional control characters, the isolating RLI/LRI/FSI with PDI characters must be supported by the application and recommended (rather than RLE/LRE with PDF) by the spec. more
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4. Use of RLM/LRM should be appropriate, and expectations of what those controls can and cannot do should be clear in the spec. more
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Detecting & matching direction (TBD)