To install this package, run in Emacs:
M-x package-install RET xref RET
This file provides a somewhat generic infrastructure for cross referencing commands, in particular "find-definition". Some part of the functionality must be implemented in a language dependent way and that's done by defining an xref backend. That consists of a constructor function, which should return a backend value, and a set of implementations for the generic functions: `xref-backend-identifier-at-point', `xref-backend-identifier-completion-table', `xref-backend-definitions', `xref-backend-references', `xref-backend-apropos', which see. A major mode would normally use `add-hook' to add the backend constructor to `xref-backend-functions'. The last three methods operate with "xref" and "location" values. One would usually call `make-xref' and `xref-make-file-location', `xref-make-buffer-location' or `xref-make-bogus-location' to create them. More generally, a location must be an instance of an EIEIO class inheriting from `xref-location' and implementing `xref-location-group' and `xref-location-marker'. There's a special kind of xrefs we call "match xrefs", which correspond to search results. For these values, `xref-match-length' must be defined, and `xref-location-marker' must return the beginning of the match. Each identifier must be represented as a string. Implementers can use string properties to store additional information about the identifier, but they should keep in mind that values returned from `xref-backend-identifier-completion-table' should still be distinct, because the user can't see the properties when making the choice. See the etags and elisp-mode implementations for full examples.