(defun fill-context-prefix (from to &optional first-line-regexp)
"Compute a fill prefix from the text between FROM and TO.
-This uses the variables `adapive-fill-prefix' and `adaptive-fill-function'.
+This uses the variables `adaptive-fill-prefix' and `adaptive-fill-function'.
If FIRST-LINE-REGEXP is non-nil, then when taking a prefix from the
first line, insist it must match FIRST-LINE-REGEXP."
(save-excursion