fix schema rules for <tr> to allow mixing <th> and <td> children within the same <tr> element as it is in the HTML5 specification
fix schema rules for <tr> to allow mixing <th> and <td> children within the same <tr> element as it is in the HTML5 specification

mushroomgithub/HTMLBook,macmillanpublishers/HTMLBook,mushroomgithub/HTMLBook,macmillanpublishers/HTMLBook,mushroomgithub/HTMLBook,gitenberg-dev/HTMLBook,oreillymedia/HTMLBook,gitenberg-dev/HTMLBook,gitenberg-dev/HTMLBook,macmillanpublishers/HTMLBook,oreillymedia/HTMLBook,oreillymedia/HTMLBook