ctags is very useful for developers to quickly look up definitions
of identifiers in the huge LO code base.

unfortunately ctags does not support the UNO IDL language,
so identifiers from the UNO API cannot be looked up yet.

likely it is not hard at all to add the required support to extract
UNO IDL definitions to ctags.

ctags website:

http://ctags.sourceforge.net

UNO IDL syntax description:

http://www.openoffice.org/udk/common/man/idl.html#object_observes_def

perhaps looking at the UNO IDL compiler may be helpful:

idlc/source/scanner.l / parser.y

or the new "unoidl" tool:

unoidl/source/sourceprovider-*