The tips here are for advanced usages of composer and its assumed you have read about using composer and have a knowledge of your vendor packages to be updated. Let's consider, you want to update only one specific yii2 vendor library, without updating all the other extension packages?
I recently had to have a checkbox column in my grid view that supported the 'disabled' attribute. This was easy enough to do by extending the CCheckBoxColumn. However, I also wanted the checkbox to be selected when clicking on the table's row (supported via CGridView's selectableRows option). I discovered I had to tweak yiigridview.js so that it would not select disabled rows when clicking on it or on the 'select all' checkbox.
Many applications wish to obtain parts of the URL for the current page (the hostname, the query string, etc.), and the CHttpRequest class wraps various $_SERVER variables to break down the URL into its constituent parts.