[1.12.1] Where to find LUA functions that are not on the API page?

[pinny]

Not sure if i'm using the right terminology, but I found some LUA functions that are not on the API page and wondering if these are documented anywhere or if people like tomrus88 just found this by reverse engineering.

The code I had seen this example was BlizzardInterfaceCode/MerchantFrame.lua at master * tomrus88/BlizzardInterfaceCode * GitHub

Here is the vanilla wow API page World of Warcraft API | Vanilla WoW Wiki | Fandom powered by Wikia

Here are some examples of what i'm talking about as seen in the example by tomrus88.

MerchantFrame:IsVisible() 
MerchantRepairAllButton:Disable();
MerchantRepairAllButton:Enable();

[ev0]

Those are XML frames, the only functions are adding IsVisible/Enable/Disable appended to them.