Philip Guenther wrote,
| For the record, procmail reads in the entire message and locates the
| head/body break before it even opens your .procmailrc (or /etc/procmailrc).
| The condition handling code then just has a pointer and length of the
| area to search, which the B and H flags and the "var ??" syntax tweak
| before handing the regexp off to the search engine.
The pointers and lengths have to get recalculated along the way, because
after a successful filtering recipe B and H (the flags and the pseudo-
variables) describe the current contents of the body and the head, not the
text at the byte offsets that the body and the head originally occupied.