Source

File: wp-includes/shortcodes.php

function shortcode_atts( $pairs, $atts, $shortcode = '' ) {
	$atts = (array) $atts;
	$out  = array();
	foreach ( $pairs as $name => $default ) {
		if ( array_key_exists( $name, $atts ) ) {
			$out[ $name ] = $atts[ $name ];
		} else {
			$out[ $name ] = $default;
		}
	}

	if ( $shortcode ) {
		/**
		 * Filters shortcode attributes.
		 *
		 * If the third parameter of the shortcode_atts() function is present then this filter is available.
		 * The third parameter, $shortcode, is the name of the shortcode.
		 *
		 * @since 3.6.0
		 * @since 4.4.0 Added the `$shortcode` parameter.
		 *
		 * @param array  $out       The output array of shortcode attributes.
		 * @param array  $pairs     The supported attributes and their defaults.
		 * @param array  $atts      The user defined shortcode attributes.
		 * @param string $shortcode The shortcode name.
		 */
		$out = apply_filters( "shortcode_atts_{$shortcode}", $out, $pairs, $atts, $shortcode );
	}

	return $out;
}