Consider merging https://chromium.googlesource.com/chromium/blink/+/f5c42430625856f4f0a711363fb5b66821314157 Per the specification, if the grid area specified for any <grid-line> doesn't exist, it should compute to 'auto'. The original parsing implementation allowed any <grid-line>, which is non-compliant. This means that "grid-row: foobar / none;" is now (again) rejected unless the grid element defines the required grid areas. The testing framework was amended to reuse the existing grid element so that we get the 'grid-template' definition as we assumed in the testing. Also added a new test that checks that unknown grid areas triggers the auto-placement algorithm when appropriate.