Это несложно. IMHO так:

^context[region;
	^sql[SELECT
			DISTINCT region.region_id AS id,
			region.name AS name
		FROM
			region, docs
		WHERE
			region.region_id = docs.region_id
		ORDER BY
			region.name
	]
	^empty[;
		<select name="region_id">
		^menu[<option value="^item[region;id]"^eq[^form[region_id];^item[region;id]; selected="selected"]>^item[region;name]</option>]
		</select>
	]
]