Today I noticed in the developer toolbar a new option - "Show Grid" / "Hide Grid"
|New Developer Toolbar Feature|
As stated in the relevant documentation - About the Developer Toolbar
Show Grid displays how regions and page items are positioned on a page if a grid layout is used.No doubt this little ditty will become extremely useful with responsive web design. Stay tuned, I'll be posting better examples as time goes on.
Thank you APEX development team.