+# b4_comment_(TEXT, OPEN, CONTINUE, END)
+# -------------------------------------
+# Put TEXT in comment. Avoid trailing spaces: don't indent empty lines.
+# Avoid adding indentation to the first line, as the indentation comes
+# from OPEN. That's why we don't patsubst([$1], [^\(.\)], [ \1]).
+#
+# Prefix all the output lines with PREFIX.
+m4_define([b4_comment_], [$2[]m4_bpatsubst([$1], [
+\(.\)], [
+$3\1])$4])
+
+
+# b4_c_comment(TEXT, [PREFIX])
+# ----------------------------
+# Put TEXT in comment. Avoid trailing spaces: don't indent empty lines.
+# Avoid adding indentation to the first line, as the indentation comes
+# from "/*". That's why we don't patsubst([$1], [^\(.\)], [ \1]).
+#
+# Prefix all the output lines with PREFIX.
+m4_define([b4_c_comment],
+[b4_comment_([$1], [$2/* ], [$2 ], [$2 */])])
+
+
+# b4_comment(TEXT, [PREFIX])
+# --------------------------
+# By default, C comments.
+m4_define([b4_comment], [b4_c_comment($@)])
+