x-select-request-type

x-select-request-type is a variable defined in `select.el'.
Its value is

nil

Documentation:
Data type request for X selection.
The value is one of the following data types, a list of them, or nil:
`COMPOUND_TEXT', `UTF8_STRING', `STRING', `TEXT'

If the value is one of the above symbols, try only the specified type.

If the value is a list of them, try each of them in the specified
order until succeed.

The value nil is the same as the list (UTF8_STRING COMPOUND_TEXT STRING).

You can customize this variable.