document return code

src/node.c

@@ -166,6 +166,8 @@ int r3_tree_compile(node *n, char **errstr)
 /**
  * This function combines ['/foo', '/bar', '/{slug}'] into (/foo)|(/bar)|/([^/]+)}
  *
+ * Return -1 if error occurs
+ * Return 0 if success
  */
 int r3_tree_compile_patterns(node * n, char **errstr) {
     char * cpat;