35067: Add (b) parameter flag for pattern char backslashing.

Doc tweak from Daniel in 35071.

Includes test.

1 files changed, 19 insertions, 0 deletions

diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo
index 85191edeb..8e5ab4bfd 100644
--- a/Doc/Zsh/expn.yo
+++ b/Doc/Zsh/expn.yo
@@ -1014,6 +1014,25 @@ form of single quoting is used that only quotes the string if needed to
 protect special characters.  Typically this form gives the most readable
 output.
 )
+item(tt(b))(
+Quote with backslashes only characters that are special to pattern
+matching. This is useful when the contents of the variable are to be
+tested using tt(GLOB_SUBST), including the tt(${~)var(...)tt(}) switch.
+
+Quoting using one of the tt(q) family of flags does not work
+for this purpose since quotes are not stripped from non-pattern
+characters by tt(GLOB_SUBST).  In other words,
+
+example(pattern=${(q)str}
+[[ $str = ${~pattern} ]])
+
+works if tt($str) is tt('a*b') but not if it is tt('a b'), whereas
+
+example(pattern=${(b)str}
+[[ $str = ${~pattern} ]])
+
+is always true for any possible value of tt($str).
+)
 item(tt(Q))(
 Remove one level of quotes from the resulting words.
 )