David Galbraith writes:
When you tag an item with a keyword such as turkey. what you are implicitly saying is category=turkey. The problem with this is that sometimes category is not enough context for a tag. Meaning always requires context. Wists allows you to label the context of a tag with anything (where the default is implicitly category). In the above example you could label something as food=turkey or country=turkey. These groups of tags, metatags allow you to indicate the context of a tag and give tags greater meaning and less ambiguity. Popular metatags that people have already created include location= for places and fav= for peoples favorite movies and books etc.
By allowing people to create metatags and attaching these metatags to their own namespace you allow for the possibility of formally defining groups of metatags as an RSS module for a specific industry. In theory one can create a marketplace for RSS modules where the people creating the modules need not know or care about the technicalities of what this means. In other words if people involved in apartment rentals start to tags things in the following manner: rooms=3 square_feet=2000 monthly_rent=2000 etc., one has the beginnings of something that could be formalized as a standard module for apartment rentals with elements defined in a standard namespace.
It is possible that these early steps in grass roots classification via tagging could evolve into something more along the lines of what the original aims of the semantic web promised.