If an HTML document has no associated doctype (e.g.
<!DOCTYPE html>), it's in quirks mode.
document.doctype === null; document.compatMode === 'BackCompat';
<meta http-equiv="X-UA-Compatible" content="IE=Edge"> won't change whether a document is in quirks mode.
For documents in quirks mode on IE/Edge, a table cell element (
<td>) that has
width: auto set explicitly will always have its
white-space computed to
normal regardless of its set value even that has
We say "has
width: auto set explicitly" here because
auto by default, while the quirk happens only when it's set explicitly.
Compare the following example on IE/Edge and another browser:
Source code of the example available here.
So the conclusion is that unless you want certain quirks mode behavior (not a good idea though), always include a valid doctype to put the document into no-quirks mode (standards mode) so that unexpected behavior won't get in the way.