Say I want to add a method somewhere that allows the parsing of an NSString into NSColor, as well as a method for printing out a NSColor into a NSString; The NSStrings have the same syntax of an SVG's color attribute. Where should I be adding these two methods? Should I write a new class "NSColorParser" and "NSColorPrinter" and add the methods there or create a new category for NSColor, adding methods "colorFromSVGAttribute:" and "svgAttributeValue"?