diff --git a/tests/scripts/generate_code.pl b/tests/scripts/generate_code.pl
index e13a2d0..750b68b 100755
--- a/tests/scripts/generate_code.pl
+++ b/tests/scripts/generate_code.pl
@@ -1,5 +1,26 @@
 #!/usr/bin/env perl
 #
+#       A test data file consists of a sequence of paragraphs separated by
+#       a single empty line. Line breaks may be in Unix (LF) or Windows (CRLF)
+#       format. Lines starting with the character '#' are ignored
+#       (the parser behaves as if they were not present).
+#
+#       Each paragraph describes one test case and must consist of: (1) one
+#       line which is the test case name; (2) an optional line starting with
+#       the 11-character prefix "depends_on:"; (3) a line containing the test
+#       function to execute and its parameters.
+#
+#       A depends_on: line consists of a list of compile-time options
+#       separated by the character ':', with no whitespace. The test case
+#       is executed only if this compilation option is enabled in config.h.
+#
+#       The last line of each paragraph contains a test function name and
+#       a list of parameters separated by the character ':'. Running the
+#       test case calls this function with the specified parameters. Each
+#       parameter may either be an integer written in decimal or hexadecimal,
+#       or a string surrounded by double quotes which may not contain the
+#       ':' character.
+#
 
 use strict;