In 4.0 : Expression Manager allow new function by plugins

I think it great if we allow too adding knowVars by plugins

But i'm unsure of what is needed, great, not needed etc …

Sample usage :
1. Q1.question for multiple choice question type.
2. Q1.help (we have it in mantis some year ago, it can help on very rare situation)
3. Q1.count, Q1.medium etc : see gitlab.com/SondagesPro/getStatInSurvey
4. API call return with specific information
5. Do some calculation with var without need to create column for this.
6. Surely a lot of other idea.


My ideas:

1. Easy way : allow adding only «fixed» string like today coreVariables (the most easy). Then : QUESTION_Q1,QUESTION_Q1_SQ1 etc … but what happen if there are QUESTION in survey
2. Only allow new fixed variable without _ (only alphabetic) : easiest but … lack of feature
3. Allow update variable part : then have Q1.question and Q1.help : think it's great but can broke a lot of things …
4. Only allow new fixed var + create own part QUESTION:Q1, QUESTION:Q1_SQ01 (like token) : think it's the cleaner but did we have all feature needed ?

If you think 2 can be great in 4.0 @Mazi or @TonisOrnisson : i make it quick with pleasure.

I like to get 4 personnaly, but make more time … did you think 3 is the best solution ?