README: document the new svgtiny_LIBCSS_ERROR code

diff --git a/README b/README
index 36f384259e222fee6e4e461f6269b7465dcba14e..de4639035b9888c49025672eef19822db8a86c62 100644 (file)
--- a/README
+++ b/README
@@ -162,8 +162,16 @@ error. The error is recorded in diagram->error_message and the line
 that caused it in diagram->error_line.
 
 svgtiny_LIBDOM_ERROR indicates that parsing the XML failed. The
-returned diagram will contain no shapes. svgtiny_NOT_SVG means that
-the XML did not contain a top-level <svg> element.
+returned diagram will contain no shapes.
+
+svgtiny_LIBCSS_ERROR indicates that something went wrong in
+libcss. Either it failed to initialize, or it failed to parse
+something within the SVG, or it failed un-initialize (free
+resources). Except in the last case, the returned diagram will be
+empty.
+
+svgtiny_NOT_SVG means that the XML did not contain a top-level
+<svg> element.
 
 To free memory used by a diagram, use svgtiny_free():