Many web apps currently use meta + enter (that is, control + enter on Windows and command + enter on OS X) as a keyboard shortcut to submit dialogs where enter already creates a new line in the dialog's text box.

Examples include:

1. Sending an email message in Gmail
2. Submitting a comment in Google Docs
3. Submitting a Facebook status (although, strangely enough, when writing a Facebook comment, the reverse is true: meta + enter creates a new line and enter submits the comment)
4. Submitting a post on Twitter.
5. Submitting a comment or task on Phabricator.
6. Saving a page in our own WikiEditor.

We should use the same shortcut in similar use cases; for example:

1. Saving input in a dialog (e.g. the citation or template dialog)
2. Saving input from inspectors with multi-line text boxes like the formula inspector
3. Saving the page itself: when the editing surface is focused, meta + enter should open the save dialog, and it should also submit the save dialog once it's open.

(As done in T125860: Provide Ctrl+Enter as a keyboard shortcut to confirm OOui dialogs for Ctrl+Enter.)