PrincipalStylesheetModule psm = importer.getPrincipalStylesheetModule();
PreparedStylesheet pss = psm.getPreparedStylesheet();
XSLStylesheet includedSheet;
StylesheetModule incModule;
DocumentURI key = DocumentFn.computeDocumentKey(href, getBaseURI());
includedSheet = psm.getStylesheetDocument(key);
if (includedSheet != null) {
// we already have the stylesheet document in cache; but we need to create a new module,
// because the import precedence might be different. See test impincl30.
incModule = new StylesheetModule(includedSheet, precedence);