Overview
ISO/IEC 10538:1991 - Information technology - Control functions for text communication specifies the set of control functions and their coded representations used when control information is embedded directly in character-coded text. The standard applies only to text made up of characters (not images) and covers two main application classes: Page‑image format (PIF) (Section 2) and formatted/formattable text (Section 3). It defines repertoires, sequences (escape and control sequences), notation, and conformance rules, but it does not define control functions for managing the communication process itself.
Key Topics and Requirements
- Repertoire of control functions: Standardizes control characters and multi‑byte control sequences used to affect layout, presentation, and navigation in character streams (examples in the text include BS, CR, LF, ESC, FF, SGR, TAB-related functions, and many PIF/formatted-text specific functions).
- Coded representations: Specifies how control functions are encoded as single bit combinations (control characters), escape sequences, or control sequences with parameters (Final/Intermediate/Parameter bytes).
- Two application profiles:
- Section 2 - Control functions for Page‑image format (PIF)
- Section 3 - Control functions for formatted and formattable text
- Conformance and levels: Defines full and limited conformance. Different selections of facilities are grouped into levels (see clauses 12 and 16); a conformance claim must identify Section and level.
- Device conformance: Originating devices must be able to supply sequences from the adopted Section/level; receiving devices must recognize and make available the corresponding control functions. A descriptive device declaration is required.
- Definitions and notation: Comprehensive terminology (e.g., CC‑data‑element, active position, formattable vs formatted text, graphic rendition).
- Scope constraint: Intended for interchange where control functions are embedded in text (not when control elements are separated into a communication protocol).
Applications and Who Uses It
- Software and systems that embed presentation or layout instructions directly in text streams (text editors, document interchange systems).
- Implementation of text renderers, printers, terminals, and display devices that must interpret or pass through control functions.
- Gateways and converters that transform between character-coded text formats while preserving embedded control semantics.
- Archivists, standards engineers, and protocol designers dealing with legacy text encodings or interoperable text interchange where embedded control functions are required.
Related Standards
- ISO 6429: Control functions for 7‑bit and 8‑bit coded character sets (many control functions are taken from ISO 6429; definitions here are generally more specific).
- ISO 2022: Code extension techniques for switching coded character sets.
- ISO 7350: Registration of graphic repertoires.
- Historical relationship with ISO 6937 parts (repertoires originally developed there).
This standard is primarily relevant where precise, interoperable control of text layout and presentation is required in the data stream-ISO/IEC 10538:1991 provides the formal vocabulary, encodings, and conformance model for that purpose.
