Merged in feature/from-pantheon (pull request #16)

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo/src/helpers/schema/html-helper.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace Yoast\WP\SEO\Helpers\Schema;
+
+/**
+ * Class HTML_Helper.
+ */
+class HTML_Helper {
+
+	/**
+	 * Sanitizes a HTML string by stripping all tags except headings, breaks, lists, links, paragraphs and formatting.
+	 *
+	 * @param string $html The original HTML.
+	 *
+	 * @return string The sanitized HTML.
+	 */
+	public function sanitize( $html ) {
+		if ( ! $this->is_non_empty_string_or_stringable( $html ) ) {
+			if ( \is_int( $html ) || \is_float( $html ) ) {
+				return (string) $html;
+			}
+
+			return '';
+		}
+
+		return \strip_tags( $html, '<h1><h2><h3><h4><h5><h6><br><ol><ul><li><a><p><b><strong><i><em>' );
+	}
+
+	/**
+	 * Strips the tags in a smart way.
+	 *
+	 * @param string $html The original HTML.
+	 *
+	 * @return string The sanitized HTML.
+	 */
+	public function smart_strip_tags( $html ) {
+		if ( ! $this->is_non_empty_string_or_stringable( $html ) ) {
+			if ( \is_int( $html ) || \is_float( $html ) ) {
+				return (string) $html;
+			}
+
+			return '';
+		}
+
+		// Replace all new lines with spaces.
+		$html = \preg_replace( '/(\r|\n)/', ' ', $html );
+
+		// Replace <br> tags with spaces.
+		$html = \preg_replace( '/<br(\s*)?\/?>/i', ' ', $html );
+
+		// Replace closing </p> and other tags with the same tag with a space after it, so we don't end up connecting words when we remove them later.
+		$html = \preg_replace( '/<\/(p|div|h\d)>/i', '</$1> ', $html );
+
+		// Replace list items with list identifiers so it still looks natural.
+		$html = \preg_replace( '/(<li[^>]*>)/i', '$1• ', $html );
+
+		// Strip tags.
+		$html = \wp_strip_all_tags( $html );
+
+		// Replace multiple spaces with one space.
+		$html = \preg_replace( '!\s+!', ' ', $html );
+
+		return \trim( $html );
+	}
+
+	/**
+	 * Verifies that the received input is either a string or stringable object.
+	 *
+	 * @param string $html The original HTML.
+	 *
+	 * @return bool
+	 */
+	private function is_non_empty_string_or_stringable( $html ) {
+		return ( \is_string( $html ) || \is_object( $html ) && \method_exists( $html, '__toString' ) ) && ! empty( $html );
+	}
+}