CKEDITOR.on( 'dialogDefinition', function( ev )
	{
		// Take the dialog name and its definition from the event
		// data.
		var dialogName = ev.data.name;
		var dialogDefinition = ev.data.definition;

		// Check if the definition is from the dialog we're
		// interested on (the "Link" dialog).
		if ( dialogName == 'link' )
		{
			// Get a reference to the "Link Info" tab.
			var infoTab = dialogDefinition.getContents( 'info' );

			// Add a text field to the "info" tab.
			infoTab.add( {
					type : 'text',
					label : 'My Custom Field',
					id : 'customField',
					'default' : 'Sample!',
					validate : function()
					{
						if ( /\d/.test( this.getValue() ) )
							return 'My Custom Field must not contain digits';
					}
				});

			// Remove the "Link Type" combo and the "Browser
			// Server" button from the "info" tab.
			infoTab.remove( 'linkType' );
			infoTab.remove( 'browse' );

			// Set the default value for the URL field.
			var urlField = infoTab.get( 'url' );
			urlField['default'] = 'www.example.com';

			// Remove the "Target" tab from the "Link" dialog.
			dialogDefinition.removeContents( 'target' );

			// Add a new tab to the "Link" dialog.
			dialogDefinition.addContents({
				id : 'customTab',
				label : 'My Tab',
				accessKey : 'M',
				elements : [
					{
						id : 'myField1',
						type : 'text',
						label : 'My Text Field'
					},
					{
						id : 'myField2',
						type : 'text',
						label : 'Another Text Field'
					}
				]
			});
		}
	});