Control Strings

Control strings are sequences of characters intended for use by the consuming application, rather than for being displayed to the user like printable characters. Control strings are of two types: character strings and command strings:

<control-string> ::= <character-string> | <command-string>

The primary difference between the two types of strings is the set of characters allowed in each.

Character Strings

Character strings are the most general type of control string. According to ECMA-48, all characters except for ControlCode.SOS (0x98), ControlCode.ST (0x9c), and their corresponding escape sequences are permitted in character strings.

Important

Here, the implmentation of AnsiStreamParser and AnsiStringParser deviates from the ECMA-48 specification. In addition to disallowing the characters mentioned above, any escape sequence and any character in the set 0x18, 0x1a, 0x80...0x9f will terminate the character string.

Characters strings can be described using the following (EBNF) notation:

<character-string>  ::= <string-initiator> <string-char>* <string-terminator>
<string-initiator>  ::= <SOS> | <ESC> <FE-SOS>
<string-char>       ::= 0x00...0x17 | 0x19 | 0x1c...0x7f | 0xa0...0xffff
<string-terminator> ::= <ST> | <ESC> <FE-ST>

<ESC>               ::= 0x1b
<FE-SOS>            ::= 0x58  // 'X'
<FT-ST>             ::= 0x5c  // '\'
<SOS>               ::= 0x98
<ST>                ::= 0x9c

Note

Character strings are terminated by an explict <string-terminator>, or by the occurence of any character not in <string-char>.

The terminal values can be referenced in code using the following symbols defined by the API:

Terminal Value	Description	API Symbol
<ESC>	Escape control code	ControlCode.ESC
<SOS>	Control code for Start of String	ControlCode.SOS
<ST>	Control code for String Terminator	ControlCode.ST
<FE-SOS>	Escape code for Start of String	EscapeCode.DCS
<FE-ST>	Escape code for String Terminator	EscapeCode.ST

Command Strings

Command strings have four different types and their content is more restricted than that of character strings, disallowing all control codes except those in the range 0x08...0x0d. They can be described using the following (EBNF) notation:

<command-string>    ::= <command-initiator> | <command-char>* <string-terminator>

<command-initiator> ::= <dcs-initiator> | <osc-initiator> | <pm-initiator> | <apc-initiator>

<dcs-initiator>     ::= <DCS> | <ESC> <FE-DCS>  // Device control string
<osc-initiator>     ::= <OSC> | <ESC> <FE-OSC>  // Operating system command
<pm-initiator>      ::= <PM>  | <ESC> <FE-PM>   // Privacy message
<apc-initiator>     ::= <APC> | <ESC> <FE-APC>  // Application program command

<command-char>      ::= 0x08...0x0d | 0x20...0x7e | 0xa0...0xffff

<string-terminator> ::= <ST> | <ESC> <FE-ST>

<ESC>    ::= 0x1b
<FE-DCS> ::= 0x50  // 'P'
<FE-OSC> ::= 0x5d  // ']'
<FE-PM>  ::= 0x5e  // '^'
<FE-APC> ::= 0x5f  // '_'
<FE-ST>  ::= 0x5c  // '\'
<DCS>    ::= 0x90
<OSC>    ::= 0x9d
<PM>     ::= 0x9e
<APC>    ::= 0x9f
<ST>     ::= 0x9c

Note

Command strings are terminated by an explict <string-terminator>, or by the occurence of any character not in <command-char>.

The terminal values can be referenced in code using the following symbols defined by the API:

Terminal Value	Description	API Symbol
<ESC>	Escape control code	ControlCode.ESC
<DCS>	Control code for a Device Control String	ControlCode.DCS
<OSC>	Control code for an Operating System Command	ControlCode.OSC
<PM>	Control code for a Privacy Message	ControlCode.PM
<APC>	Control code for an Application Program Command	ControlCode.APC
<ST>	Control code for a String Terminator	ControlCode.ST
<FE-DCS>	Escape code for a Device Control String	EscapeCode.DCS
<FE-OSC>	Escape code for an Operating System Command	EscapeCode.OSC
<FE-PM>	Escape code for a Privacy Message	EscapeCode.PM
<FE-APC>	Escape code for an Application Program Command	EscapeCode.APC
<FE-ST>	Escape code for a String Terminator	EscapeCode.ST