If you have multiple people viewing or editing the same standard at the same time in the app, the editor will warn you by adding an icon to the editor and adding a color outline around it. (If the user has added a photo or icon, you'll see that; otherwise you'll see a generic gray gravatar shape.)
If someone else has the standard open in the editor, but hasn't made any changes, you'll see the icon appear and a yellow outline will appear around the editor. You can hover your mouse over the icon to see the person who's accessing it:
If someone else has the standard open in the editor and has started making changes, you'll see the icon appear and a red outline will appear around the editor:
If one of you tries to save changes that would overwrite the changes the other one has made, you'll get a warning and can choose whether to keep your changes and overwrite the other person's, or to discard your changes and keep the other person's.