Support element.contentEditable compatibility check

Not all browsers support `isContentEditable`, some support `contentEditable` and return 'true' if the element is content editable.  This adds additional support.

I also fixed a couple of typos that I saw.

For more information see:
https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement.contentEditable
https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement.isContentEditable