[Question] What is ClientKeyValue
 

What is ClientKeyValue and when is it called ?

Re: [Question] What is ClientKeyValue
 

Where do you see this? Please provide as much context and details as possible when asking questions. If you do that then it makes it much easier to answer the question.

Generally, a Key-Value refers to a key (essentially a variable) and it's corresponding value.

Often, you can easily search for the function you're intersted in and see how other people are using to get at least some idea what it might be used for. Also, doing this will allow you to ask more specific questions.

Re: [Question] What is ClientKeyValue
 

I think he is referring to "FM_SetClientKeyValue"

Re: [Question] What is ClientKeyValue
 

Exactly

Re: [Question] What is ClientKeyValue
 

Look for plugins that already use it. Also, you can write a plugin that hooks it and then look at the results you get.

If you have something specific that you're trying to do, you should ask that. Simply asking "how does everything work" is not going to get good answer generally or they are likely already answered. Just search for info and try some stuff out.