When building the tree we generally reorder the selectors inside
the same simple selector in order to pick a good first selector
to balance the tree better. However, some kinds of selectors
can't really be reordered, even thought they are simple.
This is since the matching code for some types handle
the existance of a directly preceeding selector differently:
REGION and ANY selectors look for a DESCENDANT previous
POSITION selector look for a REGION previous
From a set of GtkCssSelectors and the rulesets they match to
we create a large decision tree that lets us efficitently match
against all the rules and return the set of matched rulesets.
The tree is created such that at each level we pick the initial rule[1]
in all the considered selectors for that level and use put the
one that is in most selectors in the node. All selectors matching that
are put in the previous part of the tree.
We now track the position as a (type,a,b) tuple where the numbers make
up the an + b formula from CSS3 nth-child.
Also, the get_sibling() and get_sibling_index() vfuncs were replaced by
a has_position() vfunc. This is mostly so that the matcher can always
return TRUE. And I need that for the everything matcher.
Previously we kept a Selector object for every "simple selector" (term
from CSS spec). Now we keep one for every match operation. So given the
selector
".a b:focus"
we will have 4 elements:
- pseudoclass ":focus"
- element "b"
- match any desendant (the space)
- class ".a"
Each of those is represented by a "selector class" which is basically
the collection of vfuncs for this selector.
'window-unfocused' is too long and mentions "focus" which is historically
loaded with the meaning "input focus".
'backdrop' isn't generally used in GUI speak and still conveys the state the
widgets in an unfocused or background toplevel window are in.
Passing the length of the widget path that is relevant is not necessary
anymore, it was only useful for inheritance. Instead, we now pass the
state flags and let the selector do the state matching for us.
