diff --git a/expat/README.md b/expat/README.md
index 762b515b..95b605a9 100644
--- a/expat/README.md
+++ b/expat/README.md
@@ -130,3 +130,62 @@ information.
 
 A reference manual is available in the file `doc/reference.html` in this
 distribution.
+
+
+The CMake build system is still *experimental* and will replace the primary
+build system based on GNU Autotools at some point when its ready.
+For an idea of the available (non-advanced) options for building with CMake:
+
+```console
+# rm -f CMakeCache.txt ; cmake -D_EXPAT_HELP=ON -LH . | grep -B1 ':.*='
+// Choose the type of build, options are: None Debug Release RelWithDebInfo MinSizeRel ...
+CMAKE_BUILD_TYPE:STRING=
+--
+// Install path prefix, prepended onto install directories.
+CMAKE_INSTALL_PREFIX:PATH=/usr/local
+--
+// Path to a program.
+DOCBOOK_TO_MAN:FILEPATH=/usr/bin/docbook2x-man
+--
+// build man page for xmlwf
+EXPAT_BUILD_DOCS:BOOL=ON
+--
+// build the examples for expat library
+EXPAT_BUILD_EXAMPLES:BOOL=ON
+--
+// build fuzzers for the expat library
+EXPAT_BUILD_FUZZERS:BOOL=OFF
+--
+// build the tests for expat library
+EXPAT_BUILD_TESTS:BOOL=ON
+--
+// build the xmlwf tool for expat library
+EXPAT_BUILD_TOOLS:BOOL=ON
+--
+// install expat files in cmake install target
+EXPAT_ENABLE_INSTALL:BOOL=ON
+--
+// Use /MT flag (static CRT) when compiling in MSVC
+EXPAT_MSVC_STATIC_CRT:BOOL=OFF
+--
+// build a shared expat library
+EXPAT_SHARED_LIBS:BOOL=ON
+--
+// Use UTF-16 encoded chars (two bytes) instead of UTF-8
+EXPAT_UNICODE:BOOL=OFF
+--
+// Use wchar_t to represent UTF-16 instead of unsigned short
+EXPAT_UNICODE_WCHAR_T:BOOL=OFF
+--
+// Treat all compiler warnings as errors
+EXPAT_WARNINGS_AS_ERRORS:BOOL=OFF
+--
+// Make use of getrandom function (ON|OFF|AUTO) [default=AUTO]
+EXPAT_WITH_GETRANDOM:STRING=AUTO
+--
+// utilize libbsd (for arc4random_buf)
+EXPAT_WITH_LIBBSD:BOOL=OFF
+--
+// Make use of syscall SYS_getrandom (ON|OFF|AUTO) [default=AUTO]
+EXPAT_WITH_SYS_GETRANDOM:STRING=AUTO
+```