I'm a bit confused by he documentation concerning \override. In most of the LR and NR it is described as a LilyPond command which changes the value of a property.
However, it also seems to appear as a special function within a \markup which adds, as opposed to changes, a property.value pair to the property list (which one isn't explicitly stated, but it can presumably be inferred from the context). Presumably the property value is removed from the list after the markup argument has been evaluated, so there is no need for a \revert command.
To sum up, am I right in thinking that within a \markup, the function supersedes the command?
I have to say, this does not feel like good program design. One does not usually have two built-in operators with the same name and different scopes. :)