code: MixinMatch match( CssFormatter formatter, List<Expression> paramValues, boolean isDefault ) {
          if( guard == null && formatter.containsRule( this ) ) {
              return null;
          }
          Map<String, Expression> mixinParameters = getMixinParams( formatter, paramValues );
          if( mixinParameters == NO_MATCH ) {
              return null;
          }
          boolean matching = true;
  
          if( guard != null ) {
              formatter.addGuardParameters( mixinParameters, isDefault );
  
              matching = guard.booleanValue( formatter );
  
              formatter.removeGuardParameters( mixinParameters );
          }
  
          return new MixinMatch( this, mixinParameters, matching, formatter.wasDefaultFunction() );
      }
docs: If this mixin match the calling parameters.
  
  @param formatter current formatter
  @param paramValues calling parameters
  @param isDefault the value of the keyword "default" in guard.
  @return the match or null if there is no match of the parameter lists