This is from my (sadly unaccepted) answer here:
https://answers.splunk.com/answers/526830/drilldown-with-click-values-not-working.html
I did something similar when I needed to search tens-of-thousands of software packages. I used 2 controls instead of one. The unusual control was a RegEx-based pre-filter on the main multi-select control:
<label>Demo for whittling down a HUGE selection list to manageable chunk</label>
<description>This is not the exact answer that you were seeking, but may be a good alternative</description>
<fieldset autorun="false" submitButton="true">
<input type="text" token="filter_token" searchWhenChanged="false">
<label>RegEx filter for Wine Dropdown --></label>
<default>.</default>
</input>
<input type="dropdown" token="wine_token" searchWhenChanged="false">
<label>(<-- filtered) Wine Selector:</label>
<default>*</default>
<choice value="*">All</choice>
<fieldForLabel>wine</fieldForLabel>
<fieldForValue>wine</fieldForValue>
<search>
<query>| inputcsv winelist.csv | regex wine="(?i)$filter_token$" | table wine</query>
<earliest>-1s</earliest>
<latest>now</latest>
</search>
</input>
</fieldset>
The really nice thing about this is that it very natural and only the geeks who grok RegEx need to know it is RegEx under the hood; the plebes will just type white and it will "just work". They will need to be taught to do red|white and that will be good for 90+% of all users/searches and for those who need more, you get to geek mentor them into RegEx.
