In order to support CLDR data, date-time pattern letters 'c' and 'e' must be added. The following is the spec of those pattern letters from LDML (Unicode Technical Standard #35).

'e' - Local day of week. Same as E except adds a numeric value that will depend on the local starting day of the week, using one or two letters. For this example, Monday is the first day of the week.

'c' - Stand-Alone local day of week - Use one letter for the local numeric value (same as 'e'), three for the short day, or four for the full name, or five for the narrow name.