Don't set intrinsic width from sizes since that's bogus. Don't set the intrinsic resolution here; we return the density and the HTML spec handles the resolution with 'current pixel density'. Fixes #121 Fixes #107
Don't allow srcset='url1,url2' in the syntax. Fixes #123
Avoid adding src to the source set when using 'w'. Fixes #119
Avoid 0/0 by banning 0 in sizes. Clarify what 0x means. Editorial fix: s/size descriptor/width descriptor/
Merge pull request #150 from zcorpan/division-by-zero

Avoid 0/0 by banning 0 in sizes. Clarify what 0x means. Editorial fix: s...
Merge pull request #147 from zcorpan/fix-119

Avoid adding src to the source set when using 'w'. Fixes #119
Bikeshed formats elementdef blocks now.
Make 0w invalid. Make sizes=0 round to a UA-specific minimum. Avoids possible discontinuities.
Merge pull request #146 from zcorpan/fix-123

Don't allow srcset='url1,url2' in the syntax. Fixes #123
Merge pull request #142 from zcorpan/fix-121-107

Don't set intrinsic width from sizes since that's bogus. Don't set the i...
Merge branch 'zero-sizes' of github.com:ResponsiveImagesCG/picture-element into zero-sizes
remove ref to zero effective size
Try out two simpler restatements of the sizes algo.
Capture the fact that only the last <source-size> can be a <length> by itself.
Bah, simple version was missing the requirement that the <media-condition> be true, and fixing that makes it cross my prose-complexity threshold.
Never mind, all the entries can be just a <length>.
Remove the simplest algo again. It really is just too simple.
Make it clearer that starting out empty triggers the step 1 condition too.
Be more explicit about what values are allowed in <source-size-value>.
Allow source sizes to go to zero.