Read a little further down. It's all in the syntax, you have to specify a property name and value.
From the org manual:
C-c a m
Match: BIB_AUTHOR="Walter Evensong"
Dear all,
I am trying to filter my entries in agenda view by properties
According to the orgmode manual, this can be done with C-c a m
However for me, C-c a m filters only on tags, not on properties. Also
the commands C-c / m and C-c \ give me an error, saying they are
undefined.
Has anybody an idea what is going on? How can I filter properties in
agenda view. and vice versa, how can I exclude a property from agenda
view?
I am running emacs 24.3.1 and orgmode 7.9.3f
Cheers,
Georg