Add basic <tab>ing ability

pretty-code-editor.php

<?php

class Pretty_Code_Editor {

	function __construct() {
		add_action( 'admin_print_styles', array( $this, 'editor_styles' ) );
		add_action( 'admin_print_footer_scripts', array( $this, 'tabs' ) );
	}

	function editor_styles() { ?>
		<style>
			#wp_mce_fullscreen, .wp-editor-area {
				font-family: "Baskerville", Georgia, Serif !important;
				font-size: 16px;
			}
		</style>
<?php }

	function tabs() { ?>
		<script>
			(function($){
				$("textarea").keydown(function(e) {
					// tab was pressed
					if(e.keyCode === 9) {
						var start = this.selectionStart,
							end = this.selectionEnd,
							$this = $(this);

						// set textarea value to: text before caret + tab + text after caret
						$this.val($this.val().substring(0, start)
									+ "\t"
									+ $this.val().substring(end));

						// put caret at right position again
						this.selectionStart = this.selectionEnd = start + 1;

						// prevent the focus lose
						return false;
					}

					// return was pressed
					else if(e.keyCode === 13) {
						var start = this.selectionStart,
							end = this.selectionEnd,
							$this = $(this),
							numTabs = countTabs($this.val(), start),
							tmp = "";
						
						// set up the value of the textarea
						tmp += $this.val().substring(0, start);
						tmp += "\n";
						for( i = 0; i < numTabs; i++)
							tmp += "\t";
						tmp += $this.val().substring(end);
						
						$this.val(tmp);
						
						// put caret at right position again
						this.selectionStart = this.selectionEnd = start + numTabs + 1;
						
						// prevent from adding an extra \n at the end
						return false;
					}
				});

				function countTabs(string, cursor) {
					var end = cursor, start;
					for (start = cursor; start >= 0 && string[start] != "\n"; --start);
					return strspn(string, "\t", start + 1, end - start + 1);
				}

				function strspn(str1, str2, start, lgth) {
					// http://kevin.vanzonneveld.net
					// +   original by: Valentina De Rosa
					// +   improved by: Brett Zamir (http://brett-zamir.me)
					// *	 example 1: strspn('42 is the answer, what is the question ...', '1234567890');
					// *	 returns 1: 2
					// *	 example 2: strspn('foo', 'o', 1, 2);
					// *	 returns 2: 2
					var found;
					var stri;
					var strj;
					var j = 0;
					var i = 0;

					start = start ? (start < 0 ? (str1.length + start) : start) : 0;
					lgth = lgth ? ((lgth < 0) ? (str1.length + lgth - start) : lgth) : str1.length - start;
					str1 = str1.substr(start, lgth);

					for (i = 0; i < str1.length; i++) {
						found = 0;
						stri = str1.substring(i, i + 1);
						for (j = 0; j <= str2.length; j++) {
							strj = str2.substring(j, j + 1);
							if (stri == strj) {
								found = 1;
								break;
							}
						}
						if (found != 1) {
							return i;
						}
					}

					return i;
				}
			})(jQuery);
		</script>
<?php }

}

new Pretty_Code_Editor();