code: protected boolean determineFeatureState(final ITemplateContext context, final IProcessableElementTag tag, final AttributeName attributeName, final String attributeValue, boolean defaultState) {
          final IStandardExpressionParser expressionParser = StandardExpressions.getExpressionParser(context.getConfiguration());
          final IStandardExpression expression = expressionParser.parseExpression(context, attributeValue);
          final Object value = expression.execute(context);
          if (value != null) {
              return isFeatureActive(value.toString());
          }
          else {
              return defaultState;
          }
      }
docs: Determines the feature state
  
  @param context        the template context
  @param tag            the tag
  @param attributeName  the attribute name
  @param attributeValue the attribute value
  @param defaultState   the default state if the expression evaluates to null
  @return the feature state