4.10. [if-field] etc.

The least-compatible things in the tag area are [if-field] (needs to be [if-PREFIX-field], where prefix might be item|loop by default depending on the tag. Likewise:

    [if-data table col]  --> [if-PREFIX-data table col]
    [on-change mark]     --> [PREFIX-change mark]
    [if-param param]     --> [if-PREFIX-param param]
    [PREFIX-param N]     --> [PREFIX-pos N] (where N is a digit)