Number - The index of the item in the current active trade skill.
String - An EnchantLink (color coded with href) which can be included in chat messages to show the reagents and the items the craft creates.
This function works with the trade skill which is currently active and only the trade skills that use the CraftFrame, not the TradeSkillFrame. Initially there is no active trade skill. A trade skill becomes active when a trade skill window is opened, for instance.
Note that not all trade skills will change the active trade skill for this function. At the moment only enchanting and hunter's train-pet window use CraftFrame. Use GetTradeSkillRecipeLink for the other professions.