+# A regular expression matching undesirable combinations of words like
+# "can not"; this matches them even when the two words appear on different
+# lines, but not when there is an intervening delimiter like "#" or "*".
+# Similarly undesirable, "See @xref{...}", since an @xref should start
+# a sentence. Explicitly prohibit any prefix of "see" or "also".
+# Also prohibit a prefix matching "\w+ +".
+# @pxref gets the same see/also treatment and should be parenthesized;
+# presume it must *not* start a sentence.
+bad_xref_re_ ?= (?:[\w,:;] +|(?:see|also)\s+)\@xref\{
+bad_pxref_re_ ?= (?:[.!?]|(?:see|also))\s+\@pxref\{
+prohibit_undesirable_word_seq_RE_ ?= \
+ /(?:\bcan\s+not\b|$(bad_xref_re_)|$(bad_pxref_re_))/gims
+prohibit_undesirable_word_seq_ = \
+ -e 'while ($(prohibit_undesirable_word_seq_RE_))' \
+ $(perl_filename_lineno_text_)
+# Define this to a regular expression that matches
+# any filename:dd:match lines you want to ignore.
+# The default is to ignore no matches.
+ignore_undesirable_word_sequence_RE_ ?= ^$$
+
+sc_prohibit_undesirable_word_seq:
+ @perl -n -0777 $(prohibit_undesirable_word_seq_) \
+ $$($(VC_LIST_EXCEPT)) \
+ | grep -vE '$(ignore_undesirable_word_sequence_RE_)' | grep . \
+ && { echo '$(ME): undesirable word sequence' >&2; exit 1; } || :