[xep-support] XEP Line Breaking Strategy

[W. Eliot Kimber]

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 
fallback.

Cheers,

E.
-- 
W. Eliot Kimber, eliot at isogen.com
Consultant, ISOGEN International

1016 La Posada Dr., Suite 240
Austin, TX  78752 Phone: 512.656.4139
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