xref-identifier-at-point-function

xref-identifier-at-point-function is a variable defined in `xref.el'.
Its value is

xref-default-identifier-at-point

• This variable may be risky if used as a file-local variable.

Documentation:
Function to get the relevant identifier at point.

The return value must be a string or nil. nil means no
identifier at point found.

If it's hard to determine the identifier precisely (e.g., because
it's a method call on unknown type), the implementation can
return a simple string (such as symbol at point) marked with a
special text property which `xref-find-function' would recognize
and then delegate the work to an external process.