Slack recently updated its message box with a WYSIWYG interface. To bold text, select it and click the "Bold" button like you're using Microsoft Word. Now, in response to criticism from some long-time users, Slack is offering a way to disable it and use classic Markdown formatting.

If you like Slack's new WYSIWYG (What You See Is What You Get) editing interface, great! It's still the default. But the new rich text editor works differently from Slack's old one, with different formatting rules. There's now a way to get back to the old text editor box, if you prefer it.

To do so, open Slack's preferences menu by clicking the menu at the top-left corner of the Slack window and selecting "Preferences."

Click "Advanced" in the left pane and enable "Format messages with markup" under Input Options.

The change will take effect immediately. As soon as you close the preferences pane, Slack's text formatting toolbar will vanish and the message box will be replaced by the old one.

By the way, Slack's message formatting isn't technically Markdown, although people call it that. Slack's "Markup" works differently from Markdown, which is why it's called something different in Slack's settings. It doesn't support all of Markdown's options.