Functions in text keys

In the same boat as you, also looking for what "placeholder" functions are actually available for text keys, specifically looking for a way to pass in a boolean into a text key and display two alternative strings, e.g. something like this:

# text key
# custom.text.key.boolean = {0,choice,true#Text when true|false#Text when false}

<#-- we then could do something like that: -->
<#assign text = text.format('custom.text.key.boolean', <boolean_variable>?c) />

this unfortunately doesn't work, but the workaround is as follows

# text key
# custom.text.key.boolean = {0,choice,0#Text when false|1#Text when true}

<#-- then do that that: -->
<#assign text = text.format('custom.text.key.boolean', <boolean_variable>?then(1, 0) />

it works, but maybe the first variant would be more pretty.

SuzieH can you point us to some documentation that explains/lists the functions available for text keys?