bibtex-summary-function is a variable defined in `bibtex.el'.
Its value is
bibtex-summary
This variable may be risky if used as a file-local variable.
Documentation:
Function to call for generating a summary of current BibTeX entry.
It takes no arguments. Point must be at beginning of entry.
Used by `bibtex-complete-crossref-cleanup' and `bibtex-copy-summary-as-kill'.
You can customize this variable.