Here is how tag syntax is defined for the most popular languages:
enum. You can tag function declarations and external variables in addition to function definitions by giving the ‘--declarations’ option to
#definemacro definitions and
enumconstants are also tags, unless you specify ‘--no-defines’ when making the tags table. Similarly, global variables are tags, unless you specify ‘--no-globals’. Use of ‘--no-globals’ and ‘--no-defines’ can make the tags table file much smaller.
operatorfunctions tags are named, for example ‘operator+’.
implementsconstructs. Tags for variables and functions in classes are named ‘class.variable’ and ‘class.function’.
\index, is a tag.
Other commands can make tags as well, if you specify them in the
TEXTAGS before invoking
value of this environment variable should be a colon-separated list of
command names. For example,
TEXTAGS="def:newcommand:newenvironment" export TEXTAGS
specifies (using Bourne shell syntax) that the commands ‘\def’, ‘\newcommand’ and ‘\newenvironment’ also define tags.
defun, any variable defined with
defconst, and in general the first argument of any expression that starts with ‘(def’ in column zero, is a tag.
defor with a construct whose name starts with ‘def’. They also include variables set with
set!at top level in the file.
Several other languages are also supported:
With Ada, it is possible to have the same name used for different entity kinds (e.g. the same name for a procedure and a function). Also, for things like packages, procedures and functions, there is the spec (i.e. the interface) and the body (i.e. the implementation). To facilitate the choice to the user, a tag value is appended with a qualifier:
So, as an example, M-x find-tag bidule/b will go directly to the body of the package bidule while M-x find-tag bidule will just search for any tag bidule.
localkeywords. Use ‘--globals’ if you want to tag global variables.
classat the beginning of a line generate a tag.
You can also generate tags based on regexp matching (see Etags Regexps) to handle other formats and languages.