Suggestions

[superpoincare]

Nice work. I have some suggestions.

html5-dom-document-php/src/HTML5DOMDocument.php

Line 371 in 3eccd3c

$html = rtrim($html, "\n");

I think this unintentionally trims newlines in the end where it isn't needed. I think your intent is to remove newline somehow added by the code before but it ends up cutting newlines elsewhere.

Another observation on this part:

html5-dom-document-php/src/HTML5DOMDocument.php

Lines 159 to 161 in 3eccd3c

	// Preserve html entities
	$source = preg_replace('/&([a-zA-Z]*);/', 'html5-dom-document-internal-entity1-$1-end', $source);
	$source = preg_replace('/&#([0-9]*);/', 'html5-dom-document-internal-entity2-$1-end', $source);

There is also an &#x type of entities. I am not sure of the following but you could check if the entity is really a genuine one or fake by doing something like

html_entity_decode( $matches[0], ENT_QUOTES, 'UTF-8' ) === $matches[0] )

with preg_replace_callback Maybe not needed.

You could also add some random string every time in the "internal" string for security purposes, maybe I am saying something silly.