User Guide

FontLab 4
678
Subtable Breaks
The implementation software will insert a subtable break within a run of
class pair rules if a single subtable cannot be created due to class overlap. A
warning will be given. For example:
pos [Ygrave] [colon semicolon] -55; # [line 99] In first subtable
pos [Y Yacute] period -50; # [line 100] In first subtable
pos [Y Yacute Ygrave] period -60; # [line 101] In second subtable
will produce a warning that a new subtable has been started at line 101,
and that some kern pairs within this subtable may never be accessed. The
pair (Ygrave, period) will have a value of 0 if the above example comprised
the entire lookup, since Ygrave is in the coverage (i.e. union of the first
glyphs) of the first subtable.
Sometimes the class kerning subtable may get too large. The editor can
force subtable breaks at appropriate points by inserting the statement:
subtable;
between two class kerning rules. The new subtable created will still be in
the same lookup, so the editor must ensure that the coverages of the
subtables thus created do not overlap. For example:
pos [Y Yacute] period -50; # In first subtable
subtable;# Force a subtable break here
pos [A Aacute Agrave] quoteright -30; # In second subtable
If the subtable statement were not present, both rules would be
represented within the same subtable.