From e0f0f80f0286b7181b1203693799f5fcfcd8b4af Mon Sep 17 00:00:00 2001
From: "Joachim Wuttke (h)" <j.wuttke@fz-juelich.de>
Date: Sun, 4 Nov 2018 23:00:12 +0100
Subject: Help: Explain conversion rules of $<BOOL:string>.

This resolves #18549.
---
 Help/manual/cmake-generator-expressions.7.rst | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/Help/manual/cmake-generator-expressions.7.rst b/Help/manual/cmake-generator-expressions.7.rst
index c5d7a31..eb9c9fe 100644
--- a/Help/manual/cmake-generator-expressions.7.rst
+++ b/Help/manual/cmake-generator-expressions.7.rst
@@ -44,8 +44,16 @@ Available boolean expressions are:
 Logical Operators
 -----------------
 
-``$<BOOL:condition>``
-  ``1`` if the ``condition`` is true, else ``0``
+``$<BOOL:string>``
+  Converts ``string`` to ``0`` or ``1`` according to the rules of the
+  :command:`if()` command.  Evaluates to ``0`` if any of the following is true:
+
+  * ``string`` is empty,
+  * ``string`` is a case-insensitive equal of
+    ``0``, ``FALSE``, ``OFF``, ``N``, ``NO``, ``IGNORE``, or ``NOTFOUND``, or
+  * ``string`` ends in the suffix ``-NOTFOUND`` (case-sensitive).
+
+  Otherwise evaluates to ``1``.
 
 ``$<AND:conditions>``
   where ``conditions`` is a comma-separated list of boolean expressions.
-- 
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