Retrieve a list of roles that the traversal rule should test for. Any node
with a role not in this list will automatically be ignored. An empty list
will match all roles. It should be assumed that this method is called once
at the start of a traversal, so changing the method’s return result after
that would have no affect.
| aRoles | [out] an array of the roles to match. |
| aCount | [out] the length of the array. |
Determines if a given accessible is to be accepted in our traversal rule
| aAccessible | [in] accessible to examine. |
| a bitfield of FILTER_MATCH and FILTER_IGNORE_SUBTREE. |
Pre-filter bitfield to filter out obviously ignorable nodes and lighten
the load on match().