You can separate very long lines contained in quotes by putting an endquote and starting a new line with a plus and opening the quote again. We use this trick in our *tinyMCE card to keep theme_advanced_buttons1 and extended_valid_elements from running off the right edge of the card:
width: '100%', auto_resize : true, relative_urls: false, theme : "advanced", theme_advanced_buttons1 : "formatselect,bold,italic," + "separator,blockquote,bullist,numlist,hr," + "separator,code,removeformat", theme_advanced_buttons2 : "", theme_advanced_buttons3 : "", theme_advanced_path :...
