=== Feature requested:
When I edit on a horizontal screen, I want to view my output next to my syntax, so I can easily check for typos and formatting.
=== Functionality/software changes
 functionality goes into Wikieditor extension of 2010 text editor
 add/adjust preview buttons and add event handlers to show or hide page preview or ineditor preview
 add breakpoints for vertical screen split editor
=== User interface changes
Ineditor Preview Inactive:
Ineditor Preview Active:
Page Preview Active:
Breakpoints (to be confirmed):
1000pt = vertical for both legacy and new vector
In new vector, the preview pane max size is 960pt as it's the size at which the readers will see the content (as shown in mocks in the Figma board below)
[[ https://www.figma.com/file/Jb6SALEoHWQRawSxscd3Ap/Wikipedia%2FLive-Preview?node-id=660%3A9334 | Figma Board ]]
=== Does this need QA?