} else if(tag.equals(MathExpressionOperatorRef.TAG)) {
express = new MathExpressionOperatorRef(element,
cf.getChildContext(MathExpressionOperatorRef.GROUP));
} else if(tag.equals(MathExpressionFunction.TAG)) {
express = new MathExpressionFunction(element,
cf.getChildContext(MathExpressionFunction.GROUP));
} else if(tag.equals(MathExpressionCoreColumnRef.TAG)) {
express = new MathExpressionCoreColumnRef(element,
cf.getChildContext(MathExpressionCoreColumnRef.GROUP));