Parse the incoming string, which is extracted from the plugin.xml file, to determine the
value of the actionType.
The string can contain one, two, or three constants. If there is more than one constant, the
constants should be separated by a comma.
These are the three constants: add, change, delete. The order that the constants are
specified in does not matter. The constants are case-sensitive; i.e., ADD is not considered
the same as add.
If the action attribute is not defined, the default behaviour is to filter in all types of
actions: add, change, delete. (i.e., the same behaviour can be achieved by specifying "add,
change, delete" as the action attribute's value.
If the action attribute is defined, and none of the constants are defined, then the filter is
invalid, and will be ignored by the Validation Framework. (If none of the actions should be
filtered in, then the filter itself should not exist.)
If the action attribute is defined, and one of the constants is defined, then the form of the
action should be like this:
<filter ... action="add"/>
If the action attribute is defined, and more than one constant is defined, then the form of
the action should be like this:
<filter ... action="add, delete"/>
If the action attribute is defined, and an unknown constant is defined, then the unknown
constant will be ignored. For example,
<filter ... action="ADD, delete"/>
is the same as specifying
<filter ... action="delete"/>
and if all of the constants are unknown, the filter is invalid, and will be ignored by the
Validation Framework. e.g.,
<filter ... action="ADD, DELETE"/>
is the same as not specifying a filter.
If the action attribute is defined, and a constant is defined more than once, the extra
constant is ignored. For example,
<filter ... action="add, change, add"/>
is the same as specifying
<filter ... action="add, change"/>