Characters can be upper (G/A/T/C) or lower (g/a/t/c) case
Rows are 50 characters wide (to facilitate identification of position if perusing). However, if the input box scrollbar appears in Chrome, Opera or Safari (sequence longer than 10 rows) rows will narrow to 48 characters until the "Count" button is activated. Coded/tested for versions of above browsers and Firefox current in Dec 2014; also for Internet Explorer 8.