TextWrangler has a strange default window setting where it won’t wrap automatically and won’t push the white background to encapsulate the overflow. Text wrapping is important on a small screen.
Text wraping is available on a per document basis via
TextWrangler > View > Text Display > Soft Wrap Text. The soft means that it won’t add line breaks into your code, it will just display lines so they don’t go off the screen. By default though, the wrapping will only expand to the page guide, or where the white ends and the gray begins, then go to the next line, it seems.
Changing the text wrapping globally is possible via
TextWrangler > Preferences > Editor Defaults. On the right, there is a checkbox with Soft wrap text a few options. My preference is Window width since full screen editing is awesome.