User-defined attributes (AST Attributes) may be attached directly to the AST. This mechanism permits the addition and removal of attribute on any node of the AST. The existence of the attributes may thus be queried from any node. The mechanism provide a way to make multiple passes over the AST and save state information into the AST for subsequent traversals. The mechanism is different from creation of inherited and synthisized attributes within the AST processing mechanism ASTProcessing, since attributes there allocated and deallocated automatically on the stack. AST Attributes are allocated on the heap and must be allocated, attached, detached, and deallocated explicitly by the used.