xref-find-definitions

[Leo Butler]

What is the name of the regexp used by xref-find-definitions to determine
the identifier? I have looked in xref.el, but I don't see any way to do
this.

Leo

PS:

  M-. runs the command xref-find-definitions (found in global-map),
  which is an autoloaded interactive compiled Lisp function in
  ‘xref.el’.
  
  It is bound to M-., <menu-bar> <edit> <goto> <xref-find-def>.
  
  (xref-find-definitions IDENTIFIER)
  
    Probably introduced at or before Emacs version 25.1.
  
  Find the definition of the identifier at point.
  With prefix argument or when there’s no identifier at point,
  prompt for it.
  
  If sufficient information is available to determine a unique
  definition for IDENTIFIER, display it in the selected window.
  Otherwise, display the list of the possible definitions in a
  buffer where the user can select from the list.