The web name of the topic that includes the current topic - same as %WEB% if there is no INCLUDE.
If a topic is used in a chain of INCLUDEs, INCLUDINGWEB is set to the topic directly INCLUDing this one, NOT the web that has been requested by the user (which is set in BASEWEB)
WARNING: While this Macro may appear to work, unless you require the subtle difference between INCLUDINGWEB and BASEWEB, you probably should use BASEWEB.