Discover 'meeting' in cat.cal:
    DOC (5): Sprint meeting
    DOC (6): London meeting with John
    DOC (1): Meeting

Discover 'london' in cat.cal:
    DOC (6): London meeting with John
    DOC (2): London calling

Discover 'john' in cat.cal:
    DOC (6): London meeting with John
    DOC (4): Beer with John