id() filtered the entire document ID index by tokens.contains on every
call, O(index) per call, so a stylesheet calling id() across a wide
document was quadratic. Look each requested token up directly in the
index dictionary instead, O(tokens). The result is unchanged: the same
elements, in document order (the ID values are the keys, each mapping to
one element). key() already used direct lookups.
Resolving 4000 id() references against a 4000-entry index drops from
about 0.34 s to about 0.03 s (~13x), now linear.
Mihaela Mihaljevic
e5b5120ac2