The history of luaTEX 2006–2009 / v 0.50 - Pragma ADE

k a el--rie am, ld p n th re, l ak ehin
aic w n.
obeying rules
When we were testing node based feature support, the only way to check this was to
identify the rules that lead to certain glyphs. The more unique glyphs are good candidates
for this. For instance
• there is s special glyph representingc/o
• in the input stream this is the character sequence c/o
• so there most be a rule that tells us that this sequence becomes that ligature
As said, in this case, the replacement glyph is supposed to be a ligature and indeed there
is such a ligature: c_slash_o. Of course, this replacement will only take place when the
sequence is surrounded by spaces.
However, when testing this, we were not looking at this rule but at the (randomly chosen)
rule that was meant to intercept the alternative h.2 followed by z.4. Interesting was that
this resolved to a ligature indeed, but the shape associated with this ligature was an h,
which is not right. Actually, a few more of such rules turned out to be wrong. It took a bit
of an effort to reach this conclusion because of the mentioned interferences of features
and rules. At that time, the rule entry (in raw LuaTEX table format) looks as follows:
[44] = {
["format"] = "coverage",
["rules"] = {
[1] = {
["coverage"] = {
["ncovers"] = {
[1] = "h.2",
[2] = "z.4",
}
},
["lookups"] = {
[1] = {
["lookup_tag"] = "L084",
["seq"] = 0,
}
}
90 Zapng fonts