added dom escape function

[hxtree]

need a way of escaping user provided data of instantiable tags for security.

This should prevent any instantiantiabled tag from being provided.

e.g. if there is an 'if' module then it should strip if tags.

[hxtree]

xpath query with process=false as used in Hoopless works to do this, but by opening and closing tags this could be circumnavigated.

[hxtree]

• Issue of user provided input containing xpath for undesirable, e.g. putting a header inside the body. It seems like we'd want to whitelist child elements.

$allowed_tags = '<p><b><br>"
addMethod([
 'xpath' => '//comments',
 'striptags' => [true, $allowed_tags]
]);

These later issues seem to be resolvable by ensure DOM structure during processing:

• Issue with user provided data containing invalid DOM structure, e.g. "Bold". This could cause the processor to fail.

• Issue with user provided data escaping parent nest, e.g. "Escape

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