Based on my previous IDL interface for XPath parsers, I've defined an API for a parser that parsers XSLT pattern expressions. It is an extension to the XPath API, so I attach only the additional functions. Any comments are appreciated. Martin module XPath{ // XSLT exprType values const unsigned short PATTERN = 17; const unsigned short LOCATION_PATTERN = 18; const unsigned short RELATIVE_PATH_PATTERN = 19; const unsigned short STEP_PATTERN = 20; interface Pattern; interface LocationPathPattern; interface RelativePathPattern; interface StepPattern; interface PatternFactory:ExprFactory{ Pattern createPattern(in LocationPathPattern first); // idkey may be null, represents IdKeyPattern // if parent is true, it is '/', else '//' // rel may be null LocationPathPattern createLocationPathPattern(in FunctionCall idkey, boolean parent, in RelativePathPattern rel); // if parent is true, it is /, else // RelativePathPattern createRelativePathPattern(in RelativePathPattern rel, boolean parent, in StepPattern step); StepPattern createStepPattern(in AxisSpecifier axis, in NodeTest test, in PredicateList predicates); }; typedef sequence<LocationPathPattern> LocationPathPatterns; interface Pattern:Expr{ readonly attribute LocationPathPatterns patterns; void append(in LocationPathPattern pattern); }; interface LocationPathPattern:Expr{ readonly attribute FunctionCall idkey; readonly attribute boolean parent; readonly attribute RelativePathPattern relative_pattern; }; interface RelativePathPattern:Expr{ readonly attribute RelativePathPattern relative; readonly attribute boolean parent; readonly attribute StepPattern step; }; interface StepPattern:Expr{ readonly attribute AxisSpecifier axis; readonly attribute NodeTest test; readonly attribute PredicateList predicates; }; interface XSLTParser:Parser{ Pattern parsePattern(in DOMString pattern); }; };