choice

Defines a set of allowed values for the field defined by the parent fielddef element.

<choice
    scope="text"
    multiple="(true|false)"
  >
  (<alternative/>+|<collection/>)
</choice>

scope="text"

Determines how the specified set of values is to be used by clients:

limit: Only the specified values are allowed.
??: The specified values are only suggestions; other values are allowed.??
??: Any more??

multiple="(true|false)"

Specifies whether or not multiple choices are allowed.