I have been using the following filter in my model for a month or two
<field name="filter_territories"
type="relation"
submit="true"
placeholder="COMPONENT_FILTER_NULL_"
label="COMPONENT_JSEARCH_TERRITORIES"
class="element-filter {{_region_region}}"
ui="chosen"
filter="array"
multiple="true"
relation="territories"
labelKey="{_region_region} - {territory}"/>
This basically gives me multi-select of (for example)
Africa - Uganda
North America - Canada
North America - United States
and each line has the region in its class i.e class="element filter Africa" which allows me to colour code
but without noticing exactly when it occurred, the {} has stopped working. I am still running 3.0.10 and I can no longer do custom labelKeys, nor use {} anywhere in the filter