extraLoader = new URLClassLoader(new URL[] { url }, contextLoader);
RegistryBuilder builder = new RegistryBuilder(extraLoader);
builder.add(TapestryModule.class);
SymbolProvider provider = new SingleKeySymbolProvider(InternalSymbols.ALIAS_MODE, "servlet");
ContributionDef contribution = new SyntheticSymbolSourceContributionDef("AliasMode", provider,
"before:ApplicationDefaults");
ModuleDef module = new SyntheticModuleDef(contribution);