-dnl This is like onceonly.m4, except that it uses diversions to named sections
-dnl DEFAULTS and INIT_PREPARE in order to check all requested headers at once,
-dnl thus reducing the size of 'configure'. Works with autoconf-2.57. The
-dnl size reduction is ca. 9%.
+dnl The original code implemented AC_CHECK_HEADERS_ONCE and AC_CHECK_FUNCS_ONCE
+dnl in terms of AC_DEFUN and AC_REQUIRE. This implementation uses diversions to
+dnl named sections DEFAULTS and INIT_PREPARE in order to check all requested
+dnl headers at once, thus reducing the size of 'configure'. It is known to work
+dnl with autoconf 2.57..2.62 at least . The size reduction is ca. 9%.