kingozorg/cleanhtml.php

## cleanhtml.php
<?php

// List of tags to be replaced and their replacement
$replace_tags = [
	'i' => 'em',
	'b' => 'strong'
];

// List of tags to be stripped. Text and children tags will be preserved.
$remove_tags = [
	'acronym',
	'applet',
	'b',
	'basefont',
	'big',
	'bgsound',
	'blink',
	'center',
	'del',
	'dir',
	'font',
	'frame',
	'frameset',
	'hgroup',
	'i',
	'ins',
	'kbd',
	'marquee',
	'nobr',
	'noframes',
	'plaintext',
	'samp',
	'small',
	'span',
	'strike',
	'tt',
	'u',
	'var'
];

// List of attributes to remove. Applied to all tags.
$remove_attribs = [
	'class',
	'style',
	'lang',
	'width',
	'height',
	'align',
	'hspace',
	'vspace',
	'dir'
];

// Your HTML code
$html = '<p class="large-font", style="color: red"><b>Hello</b> <span style="margin-left: 1em">world!</span><br>How are you doing?</p>';

function replaceTags($html, $tags) {
	// Clean the HTML
	$html = '<div>' . $html . '</div>'; // Workaround to get the HTML back from DOMDocument without the <html><head> and <body> tags
	$dom = new DOMDocument;
	$dom->loadHTML($html);
	$html = substr($dom->saveHTML($dom->getElementsByTagName('div')->item(0)), 5, -6);
	// Use simple string replace to replace tags
	foreach($tags as $search => $replace) {
		$html = str_replace('<' . $search . '>', '<' . $replace . '>', $html);
		$html = str_replace('<' . $search . ' ', '<' . $replace . ' ', $html);
		$html = str_replace('</' . $search . '>', '</' . $replace . '>', $html);
	}
	return $html;
}

function stripTags($html, $tags) {
	// Remove all attributes from tags to be removed
	$html = '<div>' . $html . '</div>';
	$dom = new DOMDocument;
	$dom->loadHTML($html);
	foreach($tags as $tag){
		$nodes = $dom->getElementsByTagName($tag);
		foreach($nodes as $node) {
			// Remove attributes
			while($node->attributes->length) {
				$node->removeAttribute($node->attributes->item(0)->name);
			}
		}
	}
	$html = substr($dom->saveHTML($dom->getElementsByTagName('div')->item(0)), 5, -6);

	// Strip tags using string replace
	foreach($tags as $tag){
		$html = str_replace('<' . $tag . '>', '', $html);
		$html = str_replace('</' . $tag . '>', '', $html);
	}

	return $html;
}

function stripAttributes($html, $attribs) {
	// Find all nodes that contain the attribute and remove it
	$html = '<div>' . $html . '</div>';
	$dom = new DOMDocument;
	$dom->loadHTML($html);
	$xPath = new DOMXPath($dom);
	foreach($attribs as $attrib) {
		$nodes = $xPath->query('//*[@' . $attrib . ']');
		foreach($nodes as $node) $node->removeAttribute($attrib);
	}
	return substr($dom->saveHTML($dom->getElementsByTagName('div')->item(0)), 5, -6);
}

$html = replaceTags($html, $replace_tags);
$html = stripTags($html, $remove_tags);
$html = stripAttributes($html, $remove_attribs);

echo $html;
	<?php

	// List of tags to be replaced and their replacement
	$replace_tags = [
	'i' => 'em',
	'b' => 'strong'
	];

	// List of tags to be stripped. Text and children tags will be preserved.
	$remove_tags = [
	'acronym',
	'applet',
	'b',
	'basefont',
	'big',
	'bgsound',
	'blink',
	'center',
	'del',
	'dir',
	'font',
	'frame',
	'frameset',
	'hgroup',
	'i',
	'ins',
	'kbd',
	'marquee',
	'nobr',
	'noframes',
	'plaintext',
	'samp',
	'small',
	'span',
	'strike',
	'tt',
	'u',
	'var'
	];

	// List of attributes to remove. Applied to all tags.
	$remove_attribs = [
	'class',
	'style',
	'lang',
	'width',
	'height',
	'align',
	'hspace',
	'vspace',
	'dir'
	];

	// Your HTML code
	$html = '<p class="large-font", style="color: red"><b>Hello</b> <span style="margin-left: 1em">world!</span><br>How are you doing?</p>';

	function replaceTags($html, $tags) {
	// Clean the HTML
	$html = '<div>' . $html . '</div>'; // Workaround to get the HTML back from DOMDocument without the <html><head> and <body> tags
	$dom = new DOMDocument;
	$dom->loadHTML($html);
	$html = substr($dom->saveHTML($dom->getElementsByTagName('div')->item(0)), 5, -6);
	// Use simple string replace to replace tags
	foreach($tags as $search => $replace) {
	$html = str_replace('<' . $search . '>', '<' . $replace . '>', $html);
	$html = str_replace('<' . $search . ' ', '<' . $replace . ' ', $html);
	$html = str_replace('</' . $search . '>', '</' . $replace . '>', $html);
	}
	return $html;
	}

	function stripTags($html, $tags) {
	// Remove all attributes from tags to be removed
	$html = '<div>' . $html . '</div>';
	$dom = new DOMDocument;
	$dom->loadHTML($html);
	foreach($tags as $tag){
	$nodes = $dom->getElementsByTagName($tag);
	foreach($nodes as $node) {
	// Remove attributes
	while($node->attributes->length) {
	$node->removeAttribute($node->attributes->item(0)->name);
	}
	}
	}
	$html = substr($dom->saveHTML($dom->getElementsByTagName('div')->item(0)), 5, -6);

	// Strip tags using string replace
	foreach($tags as $tag){
	$html = str_replace('<' . $tag . '>', '', $html);
	$html = str_replace('</' . $tag . '>', '', $html);
	}

	return $html;
	}

	function stripAttributes($html, $attribs) {
	// Find all nodes that contain the attribute and remove it
	$html = '<div>' . $html . '</div>';
	$dom = new DOMDocument;
	$dom->loadHTML($html);
	$xPath = new DOMXPath($dom);
	foreach($attribs as $attrib) {
	$nodes = $xPath->query('//*[@' . $attrib . ']');
	foreach($nodes as $node) $node->removeAttribute($attrib);
	}
	return substr($dom->saveHTML($dom->getElementsByTagName('div')->item(0)), 5, -6);
	}

	$html = replaceTags($html, $replace_tags);
	$html = stripTags($html, $remove_tags);
	$html = stripAttributes($html, $remove_attribs);

	echo $html;