Viewing Definition
Quick Definition Lookup shows you where and how your project symbols (tags, classes, methods/functions, fields, etc) are defined.
Definitions are shown in the Documentation pop-up window or in the Documentation tool window. 
For markup languages, IntelliJ IDEA retrieves definitions of symbols from the specified DTD or schema. For details, see HTML and XML.
View the definition of a symbol at caret
Select a symbol and press Ctrl+Shift+I or choose .
- Alternatively, with Ctrl/⌘ key pressed, hover your mouse pointer or the cursor over the symbol. IntelliJ IDEA displays the symbol as a link and shows its definition in a tooltip.
Quick definition tooltip shows hyperlinks to the symbols involved.
Open the definition in the Documentation tool window
In the hover mode, move your mouse pointer within the tooltip and click
in the upper-right corner.
Jump to the definition of the symbol
When in the hover mode, just click the link into which the symbol has turned.
To open the source code of the definition for editing and close the quick definition lookup window, click
on the toolbar or press F4. To open the definition without closing the quick definition lookup window, click
or press Ctrl+Enter.