safecss_filter_attr

 *
 * All hooks have default priority. The `wp_filter_kses()` function is added to
 * the 'pre_comment_content' and 'title_save_pre' hooks.
 *
 * The `wp_filter_post_kses()` function is added to the 'content_save_pre',
 * 'excerpt_save_pre', and 'content_filtered_save_pre' hooks.
 *
 * @since 2.0.0
 */
function kses_init_filters() {
	// Normal filtering.
	add_filter( 'title_save_pre', 'wp_filter_kses' );

	// Comment filtering.
	if ( current_user_can( 'unfiltered_html' ) ) {
		add_filter( 'pre_comment_content', 'wp_filter_post_kses' );
	} else {
		add_filter( 'pre_comment_content', 'wp_filter_kses' );
	}

	// Post filtering.
	add_filter( 'content_save_pre', 'wp_filter_post_kses' );
	add_filter( 'excerpt_save_pre', 'wp_filter_post_kses' );
	add_filter( 'content_filtered_save_pre', 'wp_filter_post_kses' );
}

/**
 * Removes all KSES input form content filters.
 *
 * A quick procedural method to removing all of the filters that KSES uses for
 * content in WordPress Loop.
 *
 * Does not remove the `kses_init()` function from {@see 'init'} hook (priority is
 * default). Also does not remove `kses_init()` function from {@see 'set_current_user'}
 * hook (priority is also default).
 *
 * @since 2.0.6
 */
function kses_remove_filters() {
	// Normal filtering.
	remove_filter( 'title_save_pre', 'wp_filter_kses' );

	// Comment filtering.
	remove_filter( 'pre_comment_content', 'wp_filter_post_kses' );
	remove_filter( 'pre_comment_content', 'wp_filter_kses' );

	// Post filtering.
	remove_filter( 'content_save_pre', 'wp_filter_post_kses' );
	remove_filter( 'excerpt_save_pre', 'wp_filter_post_kses' );
	remove_filter( 'content_filtered_save_pre', 'wp_filter_post_kses' );
}

/**
 * Sets up most of the KSES filters for input form content.
 *
 * First removes all of the KSES filters in case the current user does not need
 * to have KSES filter the content. If the user does not have `unfiltered_html`
 * capability, then KSES filters are added.
 *
 * @since 2.0.0
 */
function kses_init() {
	kses_remove_filters();

	if ( ! current_user_can( 'unfiltered_html' ) ) {
		kses_init_filters();
	}
}

/**
 * Filters an inline style attribute and removes disallowed rules.
 *
 * @since 2.8.1
 *
 * @param string $css        A string of CSS rules.
 * @param string $deprecated Not used.
 * @return string Filtered string of CSS rules.
 */
function safecss_filter_attr( $css, $deprecated = '' ) {
	if ( ! empty( $deprecated ) ) {
		_deprecated_argument( __FUNCTION__, '2.8.1' ); // Never implemented.
	}

	$css = wp_kses_no_null( $css );
	$css = str_replace( array( "\n", "\r", "\t" ), '', $css );

	$allowed_protocols = wp_allowed_protocols();

	$css_array = explode( ';', trim( $css ) );

	/**
	 * Filters list of allowed CSS attributes.
	 *
	 * @since 2.8.1
	 * @since 4.4.0 Added support for `min-height`, `max-height`, `min-width`, and `max-width`.
	 * @since 4.6.0 Added support for `list-style-type`.
	 * @since 5.0.0 Added support for `background-image`.
	 * @since 5.1.0 Added support for `text-transform`.
	 * @since 5.2.0 Added support for `background-position` and `grid-template-columns`.
	 * @since 5.3.0 Added support for `grid`, `flex` and `column` layout properties.
	 *              Extend `background-*` support of individual properties.
	 * @since 5.3.1 Added support for gradient backgrounds.
	 *
	 * @param string[] $attr Array of allowed CSS attributes.
	 */
	$allowed_attr = apply_filters(
		'safe_style_css',
		array(
			'background',
			'background-color',
			'background-image',
			'background-position',
			'background-size',
			'background-attachment',
			'background-blend-mode',

			'border',
			'border-radius',
			'border-width',
			'border-color',
			'border-style',
			'border-right',
			'border-right-color',
			'border-right-style',
			'border-right-width',
			'border-bottom',
			'border-bottom-color',
			'border-bottom-style',
			'border-bottom-width',
			'border-left',
			'border-left-color',
			'border-left-style',
			'border-left-width',
			'border-top',
			'border-top-color',
			'border-top-style',
			'border-top-width',

			'border-spacing',
			'border-collapse',
			'caption-side',

			'columns',
			'column-count',
			'column-fill',
			'column-gap',
			'column-rule',
			'column-span',
			'column-width',

			'color',
			'font',
			'font-family',
			'font-size',
			'font-style',
			'font-variant',
			'font-weight',
			'letter-spacing',
			'line-height',
			'text-align',
			'text-decoration',
			'text-indent',
			'text-transform',

			'height',
			'min-height',
			'max-height',

			'width',
			'min-width',
			'max-width',

			'margin',
			'margin-right',
			'margin-bottom',
			'margin-left',
			'margin-top',

			'padding',
			'padding-right',
			'padding-bottom',
			'padding-left',
			'padding-top',

			'flex',
			'flex-basis',
			'flex-direction',
			'flex-flow',
			'flex-grow',
			'flex-shrink',

			'grid-template-columns',
			'grid-auto-columns',
			'grid-column-start',
			'grid-column-end',
			'grid-column-gap',
			'grid-template-rows',
			'grid-auto-rows',
			'grid-row-start',
			'grid-row-end',
			'grid-row-gap',
			'grid-gap',

			'justify-content',
			'justify-items',
			'justify-self',
			'align-content',
			'align-items',
			'align-self',

			'clear',
			'cursor',
			'direction',
			'float',
			'list-style-type',
			'overflow',
			'vertical-align',
		)
	);

	/*
	 * CSS attributes that accept URL data types.
	 *
	 * This is in accordance to the CSS spec and unrelated to
	 * the sub-set of supported attributes above.
	 *
	 * See: https://developer.mozilla.org/en-US/docs/Web/CSS/url
	 */
	$css_url_data_types = array(
		'background',
		'background-image',

		'cursor',

		'list-style',
		'list-style-image',
	);

	/*
	 * CSS attributes that accept gradient data types.
	 *
	 */
	$css_gradient_data_types = array(