Re: [web-annotation] The textDirection and processingLanguage properties are not needed

// chair hat off

Note that Section 3.2.1 does not refer to the body of the Annotation 
itself. It contains a set of attributes that can be applied to an 
external resource. That is, to a separate file---not the Annotation 
itself. This is an important distinction, since in many cases the 
given attributes do not have an effect on the processing or 
presentation because the resource itself takes care of providing the 
necessary information.

That said, there exists an important type of resource where this is 
not true: plain text formats.

@kevinmarks Yes, text can have multiple directions. However, the 
Unicode Bidirectional Algorithm (TR9, which you mention) requires, 
among other things, a base direction with which to start. By default 
this is usually left-to-right (LTR) because most scripts are LTR. 
However, for documents containing primarily right-to-left (RTL) 
content, it is useful to have a way to set the base direction to RTL 
in cases in which the resource cannot itself set the base direction, 
such as plain text.

@halindrome That's correct, there are Unicode controls that can be 
used (and are sometimes required) in plain text to control and manage 
directionality. However, these controls may not be present in a 
resource if the base direction is supplied externally. Thus, providing
 a base direction externally may be necessary in order to ensure 
proper presentation.

@kevinmarks Regarding `processingLanguage`, this exists precisely 
because `language` is fulfilling a different purpose. The `language` 
attribute, which is allowed to appear multiple times per resource, is 
meant to indicate the intended audience(s) for the resource. Because 
it can appear 0 or more times, there is no way to set the base 
language for presenting the resource in cases where two or more 
language tags are provided and this can have an important effect on 
the intelligibility of the presentation (particularly for font 
selection in Far East languages). It is a bit of a kludge, since 
ideally `language` would take care of this.

It is the case that most document formats contain language and 
direction information (in which case, **any** external attributes 
should be ignored). But the current zoo of attributes exists to serve 
the subset of resources that cannot help themselves.

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Received on Tuesday, 2 August 2016 23:57:45 UTC