The more restrictions like this you make, the less likely you are to be matched up in a trade. The quotation marks can be left off if the product is just one word. Note that requests are not listed if they match prior offers. People making offers can specify what category they want their product to be listed under. If several different people use the same category name, a new category is created.
Categories can be hierarchical like newsgroup names.
For example, if the category clothes.kids.boys exists, then the category clothes.kids.boys.age2 can be created if enough people use that category in their offers. Or, you can indicate a second choice. If the category you want is later created, your listing will be put into it. You can also request a list of offers and requests within a given category only. However, FROM must be the last thing, since everything afterwards will be interpreted as a list of people.