A program's source text is composed of an optional UTF-8 byte-order marker followed by characters that form a sequence of symbols, white space, comments, and line terminators, up to the end of file (denoted by the EOF symbol).

The UTF-8 byte order marker is a sequence of three consecutive bytes with the values 0xEF, 0xBB, and 0xBF respectively, appearing at the beginning of a file containing EPL source text. The UTF-8 character encoding format does not need a byte-order marker to indicate the byte order because UTF-8 is by definition a bytewise encoding. A UTF-8 byte-order marker at the start of a file just indicates that the program text is encoded in the UTF-8 format. It is inserted automatically by some text editors, such as Notepad on Windows systems.

A program's source text can be encoded as Unicode UTF-8, as 7-bit ASCII (which is a proper subset of UTF-8), or various other encodings. The comiler will convert the source text from the locale's encoding to UTF-8 if necessary. In practice, this really only affects comments, white space, and string literals because all other EPL constructs are limited to the ASCII subset. Identifiers, for example, are limited to only a few of the many possible Unicode characters.