This function is implemented by FrameXML in FrameXML/ChatFrame.lua.

This function is called when a user clicks on a link in the chatframe (i.e. on an itemlink).

ChatFrame_OnHyperlinkShow(chatFrame, link, text, button)

Arguments

chatFrame 

table (Frame) - ChatFrame in which the link was clicked.

link 

String - The link component of the clicked hyperlink. (e.g. "item:6948:0:0:0...")

text 

String - The label component of the clicked hyperlink. (e.g. "[Hearthstone]")

button 

String - Button clicking the hyperlink button. (e.g. "LeftButton")