How to use link primitives such as <locus>

Hi all,
    I found that there is a few link primitives with no document about them:
        * <locus>
        * <id>
        * <hard-id>
        * <link>
        * <url> (How is this macro different from <slink>?)
        * <script> (this may be the same as <rsup>)
        * <get-binding>
        * <set-binding>
        * <has-binding>
        * <hidden-binding>
    What do these primitives mean and how to use them?
Best wishes,
jingkaimori