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
1. Submitting a comment in Google Docs
1. 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)
1. Submitting a post on Twitter.
1. Submitting a comment or task on Phabricator.
1. 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)
1. Saving input from inspectors with multi-line text boxes like the formula inspector
1. 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.