modernizr/feature-detects/css/regions.js

Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.

/*!
{
  "name": "CSS Regions",
  "caniuse": "css-regions",
  "authors": ["Mihai Balan"],
  "property": "regions",
  "tags": ["css"],
  "notes": [{
    "name": "W3C Specification",
    "href": "http://www.w3.org/TR/css3-regions/"
  }]
}
!*/
define(['Modernizr', 'createElement', 'docElement'], function( Modernizr, createElement, docElement ) {
  // We start with a CSS parser test then we check page geometry to see if it's affected by regions
  // Later we might be able to retire the second part, as WebKit builds with the false positives die out

  Modernizr.addTest('regions', function() {

    /* Get the 'flowFrom' property name available in the browser. Either default or vendor prefixed.
       If the property name can't be found we'll get Boolean 'false' and fail quickly */
    var flowFromProperty = Modernizr.prefixed("flowFrom");
    var flowIntoProperty = Modernizr.prefixed("flowInto");

    if (!flowFromProperty || !flowIntoProperty){
      return false;
    }

    /* If CSS parsing is there, try to determine if regions actually work. */
    var container = createElement('div');
    var content = createElement('div');
    var region = createElement('div');

    /* we create a random, unlikely to be generated flow number to make sure we don't
       clash with anything more vanilla, like 'flow', or 'article', or 'f1' */
    var flowName = 'modernizr_flow_for_regions_check';

    /* First create a div with two adjacent divs inside it. The first will be the
       content, the second will be the region. To be able to distinguish between the two,
       we'll give the region a particular padding */
    content.innerText = 'M';
    container.style.cssText = 'top: 150px; left: 150px; padding: 0px;';
    region.style.cssText = 'width: 50px; height: 50px; padding: 42px;';

    region.style[flowFromProperty] = flowName;
    container.appendChild(content);
    container.appendChild(region);
    docElement.appendChild(container);

    /* Now compute the bounding client rect, before and after attempting to flow the
       content div in the region div. If regions are enabled, the after bounding rect
       should reflect the padding of the region div.*/
    var flowedRect, delta;
    var plainRect = content.getBoundingClientRect();


    content.style[flowIntoProperty] = flowName;
    flowedRect = content.getBoundingClientRect();

    delta = parseInt(flowedRect.left - plainRect.left, 10);
    docElement.removeChild(container);
    content = region = container = undefined;

    return (delta == 42);
  });
});