The cache, as implemented currently, was implemented to achief a boost of (iirc) about 25%. It is needed to reduce the access to the object (the $self hash), as those lookups are very very expensive.

Unicode whitespace isn't important for this parser, as it is no special "character", unless it being the separator, the quotation or the escape character. Unicode whitespace will just end up being binary.

XS is not PP :) Those characters could be int indeed, but that would probably mean that the whole parser (written in 1998 and modified/extended over time) has to be rewritten. It /might/ be worth the effort in the end, but I do not have the time to start that experiment.

Never tried fsm (unless the current state-machine already is an FSM). I simplified the parser as I got it when I took over maint. Over time a lot of bugs were fixed and new (required and requested) features where added.

update: added remark about FSM