WordPress Shortcode Boilerplate

<?php

/**
 * WordPress Shortcode Boilerplate.
 *
 * Shortcode functions accepts the following parameters:
 *
 * $atts (array) : When a user writes a shortcode into their WordPress post
 * which triggers your shortcode function, any attributes they assign to that
 * shortcode will be passed as an associative array to your function. For
 * example the shortcode [caption caption="foobar"] would result in an $atts
 * being assigned the associative array "array( 'caption' => 'foobar')"
 *
 * $content (string) : The content of the shortcode.  Like HTML tags a
 * shortcode can be either self-terminating (like the <img/> tag) or provide
 * opening and closing tags (like <p>...</p>). When a shortcode provides an
 * opening and closing tag, $content is assigned the data between the tags.
 * For example if we write the following shortcode [caption]This is the
 * content of my shortcode[/caption], $content would be assigned the string
 * "This is the content of my shortcode"
 *
 * $tag (string) : The name of the shortcode that triggered the function.
 * Multiple shortcodes can actually be assigned the same function, and $tag
 * allows us to determine programmatically which shortcode triggered the
 * function. For example we might create a function called headers() and
 * assign it to the shortcodes h1, h2, h3, h4, h5, h6. Using the shortcode
 * [h1]...[/h1] would call headers() with $tag being assigned the value "h1",
 * [h2]...[/h2] would call headers() with $tag being assigned the value "h2",
 * etc.
 *
 * Shortcode functions return a value. They do not output text.
 *
 * @param array  $atts    Attributes assigned to the shortcode.
 * @param string $content The text between the opening and closing tags.
 * @param string $tag     The shortcode tag that triggered the function.
 *
 * @return string Returns the text generated by the shortcode.
 */
function shortcode_func( $atts, $content = null, $tag = '' )
{
    /*
     * The following lines utilize the shortcode_atts() WordPress function
     * to mix-in default values for your shortcode's attributes.  For
     * example if your shortcode accepts an attribute named "foo" it will
     * be assigned the value "something" if the user did not specify a
     * value.
     *
     * The PHP extract() function is then used to convert the shortcode's
     * attributes into local variables. So we can refer to the "foo"
     * attribute by checking the variable $foo rather than referring to
     * $atts['foo'].
     */
    extract( shortcode_atts( array(
        'foo' => 'something',
        'bar' => 'something else'
    ), $atts ) );

    /*
     * This is where we do custom processing for our shortcode. I'm just
     * assigning the variable $html the content of the shortcode. The code
     * that falls here is totally up to you.
     */
    $html = $content;

    /*
     * Process any nested shortcodes and return our processed data. If your
     * shortcode has a start and end tag and contains content, this step is
     * neccessary, otherwise nested shortcodes may display unprocessed to
     * your readers!
     */
    return do_shortcode( $html );
}

/*
 * Use the WordPress add_shortcode() function to register a shortcode with
 * WordPress. The first parameter specifies the shortcode tag that will be
 * used to trigger your function. The second parameter specifies the name
 * of the function to call when the shortcode is encountered.
 */
add_shortcode( 'shortcode', 'shortcode_func' );