All of the descriptive elements support the type attribute. This is a value that expresses the purpose or context of the element it is applied to. If two elements have the same type then the information that each contains should be interpretted as being connected in some way. There are no restrictions on the format and value of the type attribute so any Supplier cannot utilise any type that they wish to. However, unless the Consumer knows what meaning to attribute to the type then it doesn't server any purpose.
The decision to keep the type format so open is intentional. While it does limit the ability for the schema to enforce well behaved usage of a standard type structure, it permits the expansion of the system without having to re-release new versions of the schema for each expansion.
In general the type will generally be one of the following three types: