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<div class="moz-cite-prefix">On 16092020 3:30 pm, Peter Constable
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:MWHPR1301MB2112644575A0E080AB4AD1CD86210@MWHPR1301MB2112.namprd13.prod.outlook.com">
<p class="MsoNormal">“In recommended usage, the application
applies this feature automatically to characters at the right
end of a horizontal line when the 'opbd' feature
has been applied to those characters. See the the
['opbd'](#opbd) feature for additional
information.”<o:p></o:p><o:p> </o:p>
</p>
<p class="MsoNormal">To allow for usage of ‘lfbd’ or ‘rtbd’
independent of ‘opbd’, I’ve have to revise that, but that would
be doable.</p>
</blockquote>
<p>Note that an actual implementation would throw up a number of
interesting practical issues. The lfbd and rtbd features should be
applied, respectively, when text is left-aligned or right-aligned.
That would imply not only margin alignment, but also column
alignment, and even tab alignment. While margin and column widths
may reasonably be assumed to be wide enough to merit text boundary
alignment, tab distances may be close, and it may be necessary for
software to use some kind of tolerance when determining whether to
apply a boundary alignment feature.</p>
<p>If text is justified (i.e. both left and right boundaries are
aligned to margin, column edges, etc..) the output of the lfbd and
rtbd features needs to be taken into account for linebreaking and
other justification functions such as wordspacing tolerances or
kashida insertion.</p>
<p><br>
</p>
<p>Because of the amount of work involved in defining lfbd and rtbd
GPOS lookups (and the current lack of any very convenient visual
editing tool), I don't imagine it being something a lot of font
makers would do for a lot of fonts (although that may be different
if automated (paging Mr Cozens)). I can imagine it being most
desirable in some display fonts with unusual glyph shapes,
extending left and right swashes intended for line initial and
final use, and similar things that don't submit well to
algorithmic text boundary alignment.<br>
</p>
<p>JH<br>
</p>
<pre class="moz-signature" cols="72">--
John Hudson
Tiro Typeworks Ltd <a class="moz-txt-link-abbreviated" href="http://www.tiro.com">www.tiro.com</a>
Salish Sea, BC <a class="moz-txt-link-abbreviated" href="mailto:tiro@tiro.com">tiro@tiro.com</a>
NOTE: In the interests of productivity, I am currently
dealing with email on only two days per week, usually
Monday and Thursday unless this schedule is disrupted
by travel. If you need to contact me urgently, please
use some other method of communication. Thank you.</pre>
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