How the micro-blogging site has changed
If a tweeted URL is recognised as containing an image or video, that media can be viewed on the right by clicking the media icon; clicking the left arrow then collapses this panel, changing the right pane back to its original look.
Twitter: Creating tweets
Tweets can be made from the box at the top of the timeline, or by clicking the pen icon (in the upper right) to get this pop-up window.
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