regex101 Conditional statement is always else

I am using http://www.regexr.com/ and https://regex101.com/ to learn regex

regex101's Quick reference shows

Conditional statement: (?(...)|)

If the given pattern matches, matches the pattern before the vertical bar. Otherwise, matches the pattern after the vertical bar.

I can't get it to work at all

/(^(?!no)if|else)/gm

no if else

yes if else

looks like its broken

/(?:(yes)true|false)/g

yes true false

I need to return a single match using string.match so I stay compatible with a third party. I don't have the option to do anything with the results myself so I won't be able to do multiple regex nor filter results with javascript. what I would like to achive is a regex that asks for

if the sentence starts with the word 'name' or the sentence contains '.classX' then return nothing else return '.classA'

returning eather [""] or [".classA "]

Is this possible at all or am I completly waisting my time?