public HighlightingDefinition AddSpan(string startExpression, string endExpression, Color color, FontWeight? fontWeight = null)
 {
     return AddSpan(startExpression, endExpression, color.ToHighlightingColor(fontWeight));
 }
 public HighlightingDefinition AddRule(string expression, Color color, FontWeight? fontWeight = null)
 {
     return AddRule(expression, color.ToHighlightingColor(fontWeight));
 }