Many bridges implemented getDescription() which is only applicable for
bridges extending RSSExpander.
Functions that are not part of the abstract class or interface should
be in private scope for better readability.
This fixes error "Using $this when not in object context"
Nested functions are not part of the object and therefore don't have
access to the object instance $this!
This also fixes an error where calling collectData multiple times would
result in an attempt to redeclare all nested functions (which would
cause errors)
