__init__ (
        self,
        name,
        expression,
        attrs=None,
        )

(name, expression)

Create a group named name which matches the given expression

__str__ ( self )

the corresponding pattern string

_find_groups ( self,  tag )

return a list of all groups matching the given tag

_select_names ( self,  names )

internal function: do not use

copy ( self )

do a deep copy on this Expression tree

features ( self )

return a list of all features

group_names ( self )

the list of group names used by this Expression and its children