[xep-support] XEP Line Breaking Strategy

From: W. Eliot Kimber (eliot@isogen.com)
Date: Sat Nov 16 2002 - 13:52:10 PST

Attached is a small hyphenation sample document. As part of this sample
I created some areas with text that won't fit into the IPD if rendered
"normally." When hyphenation is on, XEP and XSL Formatter produce
equally nice results (although I think XEP does a slightly nicer job in
this case. Also, XSL Formatter fails to balance the columns in this
sample, while XEP balances them perfectly--not sure why XSL Formatter
falls down there).

But, when hyphentation is off, the XEP result is not always better.

In the case where the mismatch is relatively small (the second block in
the first column), XEP's result is quite nice--it squeezes the character
kerning just enough to fit the long word. By contrast, XEP breaks the
word following one of the dashes. FOP just lets the text run into the
next column (ouch). I guess you could characterize XSL Formatter's
behavior as "hyphenate if you have to, even if hyphenation is off" (that
is, "do what I need, not what I asked for").

However, when the mismatch is greater (the 4th block), the XEP result is
an unreadable jumble of overlaid letters, while the XSL Formatter result
continues to be readable (because it breaks the word).

I'm wondering if it's possible for XEP to fall back to the XSL behavior
when the kerning goes negative (that is, the characters overprint each
other)? That would provide the best of both implementations--the best
result when just a little squeezing will fix it, a readable result when
it won't.

I realize that having this type of situation is fundamentally user
error, but it's also the case that the XSL Formatter behavior does
ensure that the result is always readable, even if it's not always what
was desired.

It seems clear from the spec that line breaking algorithms are entirely
  up to implementors, so there's no issue of conformance or
non-conformance in this case--it's just an issue of aesthetics and



W. Eliot Kimber, eliot@isogen.com
Consultant, ISOGEN International
1016 La Posada Dr., Suite 240
Austin, TX  78752 Phone: 512.656.4139

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