The character escaping facility is prescribed by the ISO Prolog standard, and allows escape sequences to occur within strings and quoted atoms, so that programmers can put non-printable characters in atoms and strings and still be able to see what they are doing.
Strings or quoted atoms containing escape sequences can occur in terms
obtained by read/[1,2], compile/1, and so on.
The ‘0'’ notation for the integer code of a character is also affected by
character escaping.
The only characters that can occur in a string or quoted atom are the printable characters and <SPC>. All other layout characters must be expressed with escape sequences (see ref-syn-syn-esc).