String::Tagged::Formatting - an API specification for simple formatted strings


A primary use case of String::Tagged is to allow storage of a text string with associated formatting data. As there are a growing number of subclasses on CPAN that attempt to do this, a common specification is emerging to allow interoperability between them. This will allow interchange between formats from different sources, display or rendering, and so on.

Primarily this specification consists of the names and meanings of a set of tags that a conforming string should supply, though it also suggests a pair of methods useful for converting between different types of object and the standard formatting. Specific implementations may not be able to represent all of the tags of course; this specification only gives the suggested way to represent those formatting styles that the implementation actually understands.


bold, under, italic, strike, blink, monospace

Tags with boolean values indicating bold, underline, italic, strikethrough, blinking and monospaced font.


Tag with boolean value indicating reverse video; i.e. the effect of swapping foreground and background colours. This effect is common on terminal-based string systems, but is unlikely to be found elsewhere.

fg, bg

Tags with Convert::Color instances giving foreground and background colours. The use of a Convert::Color instance allows specific implementations to be able to represent their own colour space, while still supporting an easy conversion to the colour spaces used by others.


The following methods should be provided on conforming implementations, to indicate their support of this specification and to allow easy conversion from and to it.


  $fmt = $st->as_formatting

Called on an existing instance of the class, returns a String::Tagged instance (or some subclass thereof) containing only the tags and values defined by this specification. This method may simply return the original instance if the tags natively used by it already fit this specification, or it may return a newly-constructed instance by converting its own tag formats.

Use of the clone method with only_tags and possibly a convert_tags map should be able to implement this in most cases.


  $st = String::Tagged::Subclass->new_from_formatting( $fmt )

Called as a class method on the target class type, returns a new instance of that class constructed to represent the formatting contained in the $fmt instance, which should contain only the tags given in this specification. If the class natively uses tags as per this specification, this can be a trivial clone, otherwise some conversion will need to be performed.

Use of the clone method with only_tags and possibly a convert_tags map should be able to implement this in most cases.


  • Net::Async::Matrix::Utils - Contains a pair of functions to convert a formatted Matrix message body to and from this format.

  • String::Tagged::IRC - parse or build IRC formatted messages and convert bidirectionally to this format.

  • String::Tagged::Terminal - build terminal control sequences for message formatting and convert bidirectionally to this format.


Paul Evans <>