StyledStrings · The Julia Language
Description: Documentation for The Julia Language.

# StyledStrings

Note

The API for StyledStrings and AnnotatedStrings is considered experimental and is subject to change between Julia versions.

## Styling

When working with strings, formatting and styling often appear as a secondary concern.

For instance, when printing to a terminal you might want to sprinkle ANSI escape sequences in the output, when outputting HTML styling constructs (`<span style="...">`, etc.) serve a similar purpose, and so on. It is possible to simply insert the raw styling constructs into the string next to the content itself, but it quickly becomes apparent that this is not well suited for anything but the most basic use cases. Not all terminals support the same ANSI codes, the styling constructs need to be painstakingly removed when calculating the width of already-styled content, and that's before you even get into handling multiple output formats.

Instead of leaving this headache to be widely experienced downstream, it is tackled head-on by the introduction of a special string type (`AnnotatedString`). This string type wraps any other `AbstractString` type and allows for formatting information to be applied to regions (e.g. characters 1 through to 7 are bold and red).

Regions of a string are styled by applying `Face`s (think "typeface") to them — a structure that holds styling information. As a convenience, faces in the global faces dictionary (e.g. `shadow`) can just be named instead of giving the `Face` directly.

Along with these capabilities, we also provide a convenient way for constructing `AnnotatedString`s, detailed in Styled String Literals.

    julia> using StyledStrings
    julia> styled"{yellow:hello} {blue:there}""hello there"

## Annotated Strings

It is sometimes useful to be able to hold metadata relating to regions of a string. A `AnnotatedString` wraps another string and allows for regions of it to be annotated with labelled values (`:label => value`). All generic string operations are applied to the underlying string. However, when possible, styling information is preserved. This means you can manipulate a `AnnotatedString` —taking substrings, padding them, concatenating them with other strings— and the metadata annotations will "come along for the ride".

This string type is fundamental to the StyledStrings stdlib, which uses `:face`-labelled annotations to hold styling information.

When concatenating a `AnnotatedString`, take care to use `annotatedstring` instead of `string` if you want to keep the string annotations.

    julia> str = AnnotatedString("hello there", [(1:5, :word, :greeting), (7:11, :label, 1)])
    "hello there"

    julia> length(str)
    11

    julia> lpad(str, 14)
    "   hello there"

    julia> typeof(lpad(str, 7))
    AnnotatedString{String}

    julia> str2 = AnnotatedString(" julia", [(2:6, :face, :magenta)])
    " julia"

    julia> annotatedstring(str, str2)
    "hello there julia"

    julia> str * str2 == annotatedstring(str, str2) # *-concatenation works
    true

The annotations of a `AnnotatedString` can be accessed and modified via the `annotations` and `annotate!` functions.

## Styling via `AnnotatedString`s

## Faces

### The `Face` type

A `Face` specifies details of a typeface that text can be set in. It covers a set of basic attributes that generalize well across different formats, namely:

- `font`
- `height`
- `weight`
- `slant`
- `foreground`
- `background`
- `underline`
- `strikethrough`
- `inverse`
- `inherit`

For details on the particular forms these attributes take, see the `Face` docstring, but of particular interest is `inherit` as it allows you to inherit attributes from other `Face`s.

### The global faces dictionary

To make referring to particular styles more convenient, there is a global `Dict{Symbol, Face}` that allows for `Face`s to be referred to simply by name. Packages can add faces to this dictionary via the `addface!` function, and the loaded faces can be easily customized.

Appropriate face naming

Any package registering new faces should ensure that they are prefixed by the package name, i.e. follow the format `mypackage_myface`. This is important for predictability, and to prevent name clashes.

Furthermore, packages should take care to use (and introduce) semantic faces (like `code`) over direct colours and styles (like `cyan`). This is helpful in a number of ways, from making the intent in usage more obvious, aiding composability, and making user customisation more intuitive.

There are two set of exemptions to the package-prefix rule:

- the set of basic faces that are part of the default value of the faces dictionary
- faces introduced by Julia's own standard library, namely `JuliaSyntaxHighlighting`

#### Basic faces

Basic faces are intended to represent a general idea that is widely applicable.

For setting some text with a certain attribute, we have the `bold`, `light`, `italic`, `underline`, `strikethrough`, and `inverse` faces.

There are also named faces for the 16 terminal colors: `black`, `red`, `green`, `yellow`, `blue`, `magenta`, `cyan`, `white`, `bright_black`/`grey`/`gray`, `bright_red`, `bright_green`, `bright_blue`, `bright_magenta`, `bright_cyan`, and `bright_white`.

For shadowed text (i.e. dim but there) there is the `shadow` face. To indicate a selected region, there is the `region` face. Similarly for emphasis and highlighting the `emphasis` and `highlight` faces are defined. There is also `code` for code-like text.

For visually indicating the severity of messages, the `error`, `warning`, `success`, `info`, `note`, and `tip` faces are defined.

### Customisation of faces (`Faces.toml`)

It is good for the name faces in the global face dictionary to be customizable. Theming and aesthetics are nice, and it is important for accessibility reasons too. A TOML file can be parsed into a list of `Face` specifications that are merged with the pre-existing entry in the face dictionary.

A `Face` is represented in TOML like so:

    [facename]
    attribute = "value"
    ...

    [package.facename]
    attribute = "value"

For example, if the `shadow` face is too hard to read it can be made brighter like so:

    [shadow]
    foreground = "white"

On initialization, the `config/faces.toml` file under the first Julia depot (usually `~/.julia`) is loaded.

### Applying faces to a `AnnotatedString`

By convention, the `:face` attributes of a `AnnotatedString` hold information on the `Face`s that currently apply. This can be given in multiple forms, as a single `Symbol` naming a `Face`s in the global face dictionary, a `Face` itself, or a vector of either.

The `show(::IO, ::MIME"text/plain", ::AnnotatedString)` and `show(::IO, ::MIME"text/html", ::AnnotatedString)` methods both look at the `:face` attributes and merge them all together when determining the overall styling.

We can supply `:face` attributes to a `AnnotatedString` during construction, add them to the properties list afterwards, or use the convenient Styled String literals.

    julia> str1 = AnnotatedString("blue text", [(1:9, :face, :blue)])"blue text"
    julia> str2 = styled"{blue:blue text}""blue text"
    julia> str1 == str2true
    julia> sprint(print, str1, context = :color => true)"\e[34mblue text\e[39m"
    julia> sprint(show, MIME("text/html"), str1, context = :color => true)"<span style=\"color: #195eb3\">blue text</span>"

## Styled String Literals

To ease construction of `AnnotatedString`s with `Face`s applied, the `styled"..."` styled string literal allows for the content and attributes to be easily expressed together via a custom grammar.

Within a `styled"..."` literal, curly braces are considered special characters and must be escaped in normal usage (`\{`, `\}`). This allows them to be used to express annotations with (nestable) `{annotations...:text}` constructs.

The `annotations...` component is a comma-separated list of three types of annotations.

- Face names
- Inline `Face` expressions `(key=val,...)`
- `key=value` pairs

Interpolation is possible everywhere except for inline face keys.

For more information on the grammar, see the extended help of the `styled"..."` docstring.

As an example, we can demonstrate the list of built-in faces mentioned above like so:

    julia> println(styled"
    The basic font-style attributes are {bold:bold}, {light:light}, {italic:italic},
    {underline:underline}, and {strikethrough:strikethrough}.

    In terms of color, we have named faces for the 16 standard terminal colors:
     {black:■} {red:■} {green:■} {yellow:■} {blue:■} {magenta:■} {cyan:■} {white:■}
     {bright_black:■} {bright_red:■} {bright_green:■} {bright_yellow:■} {bright_blue:■} {bright_magenta:■} {bright_cyan:■} {bright_white:■}

    Since {code:bright_black} is effectively grey, we define two aliases for it:
    {code:grey} and {code:gray} to allow for regional spelling differences.

    To flip the foreground and background colors of some text, you can use the
    {code:inverse} face, for example: {magenta:some {inverse:inverse} text}.

    The intent-based basic faces are {shadow:shadow} (for dim but visible text),
    {region:region} for selections, {emphasis:emphasis}, and {highlight:highlight}.
    As above, {code:code} is used for code-like text.

    Lastly, we have the 'message severity' faces: {error:error}, {warning:warning},
    {success:success}, {info:info}, {note:note}, and {tip:tip}.

    Remember that all these faces (and any user or package-defined ones) can
    arbitrarily nest and overlap, {region,tip:like {bold,italic:so}}.")

     The basic font-style attributes are bold, light, italic,
     underline, and strikethrough.

     In terms of color, we have named faces for the 16 standard terminal colors:
      ■ ■ ■ ■ ■ ■ ■ ■
      ■ ■ ■ ■ ■ ■ ■ ■

     Since bright_black is effectively grey, we define two aliases for it:
     grey and gray to allow for regional spelling differences.

     To flip the foreground and background colors of some text, you can use the
     inverse face, for example: some inverse text.

     The intent-based basic faces are shadow (for dim but visible text),
     region for selections, emphasis, and highlight.
     As above, code is used for code-like text.

     Lastly, we have the 'message severity' faces: error, warning,
     success, info, note, and tip.

     Remember that all these faces (and any user or package-defined ones) can
     arbitrarily nest and overlap, like so.

## API reference

### Styling and Faces

`StyledStrings.StyledMarkup.@styled_str` — Macro

    @styled_str -> AnnotatedString

Construct a styled string. Within the string, `{<specs>:<content>}` structures apply the formatting to `<content>`, according to the list of comma-separated specifications `<specs>`. Each spec can either take the form of a face name, an inline face specification, or a `key=value` pair. The value must be wrapped by `{...}` should it contain any of the characters `,=:{}`.

String interpolation with `$` functions in the same way as regular strings, except quotes need to be escaped. Faces, keys, and values can also be interpolated with `$`.

Example

    styled"The {bold:{italic:quick} {(foreground=#cd853f):brown} fox} jumped over the {link={https://en.wikipedia.org/wiki/Laziness}:lazy} dog"

Extended help

This macro can be described by the following EBNF grammar:

    styledstring = { styled | interpolated | escaped | plain } ;

    specialchar = '{' | '}' | '$' | '\"' ;
    anychar = [\u0-\u1fffff] ;
    plain = { anychar - specialchar } ;
    escaped = '\\', specialchar ;

    interpolated = '$', ? expr ? | '$(', ? expr ?, ')' ;

    styled = '{', ws, annotations, ':', content, '}' ;
    content = { interpolated | plain | escaped | styled } ;
    annotations = annotation | annotations, ws, ',', ws, annotation ;
    annotation = face | inlineface | keyvalue ;
    ws = { ' ' | '\t' | '\n' } ; (* whitespace *)

    face = facename | interpolated ;
    facename = [A-Za-z0-9_]+ ;

    inlineface = '(', ws, [ faceprop ], { ws, ',', faceprop }, ws, ')' ;
    faceprop = [a-z]+, ws, '=', ws, ( [^,)]+ | interpolated) ;

    keyvalue = key, ws, '=', ws, value ;
    key = ( [^\0${}=,:], [^\0=,:]* ) | interpolated ;
    value = simplevalue | curlybraced | interpolated ;
    curlybraced = '{' { escaped | plain } '}' ;
    simplevalue = [^${},:], [^,:]* ;

An extra stipulation not encoded in the above grammar is that `plain` should be a valid input to `unescape_string`, with `specialchar` kept.

The above grammar for `inlineface` is simplified, as the actual implementation is a bit more sophisticated. The full behaviour is given below.

    faceprop = ( 'face', ws, '=', ws, ( ? string ? | interpolated ) ) |
               ( 'height', ws, '=', ws, ( ? number ? | interpolated ) ) |
               ( 'weight', ws, '=', ws, ( symbol | interpolated ) ) |
               ( 'slant', ws, '=', ws, ( symbol | interpolated ) ) |
               ( ( 'foreground' | 'fg' | 'background' | 'bg' ),
                   ws, '=', ws, ( simplecolor | interpolated ) ) |
               ( 'underline', ws, '=', ws, ( underline | interpolated ) ) |
               ( 'strikethrough', ws, '=', ws, ( bool | interpolated ) ) |
               ( 'inverse', ws, '=', ws, ( bool | interpolated ) ) |
               ( 'inherit', ws, '=', ws, ( inherit | interpolated ) ) ;

    nothing = 'nothing' ;
    bool = 'true' | 'false' ;
    symbol = [^ ,)]+ ;
    hexcolor = ('#' | '0x'), [0-9a-f]{6} ;
    simplecolor = hexcolor | symbol | nothing ;

    underline = nothing | bool | simplecolor | underlinestyled;
    underlinestyled = '(', ws, ('' | nothing | simplecolor | interpolated), ws,
                      ',', ws, ( symbol | interpolated ), ws ')' ;

    inherit = ( '[', inheritval, { ',', inheritval }, ']' ) | inheritval;
    inheritval = ws, ':'?, symbol ;

source
`StyledStrings.StyledMarkup.styled` — Function

    styled(content::AbstractString) -> AnnotatedString

Construct a styled string. Within the string, `{<specs>:<content>}` structures apply the formatting to `<content>`, according to the list of comma-separated specifications `<specs>`. Each spec can either take the form of a face name, an inline face specification, or a `key=value` pair. The value must be wrapped by `{...}` should it contain any of the characters `,=:{}`.

This is a functional equivalent of the `@styled_str` macro, just without interpolation capabilities.

source
`StyledStrings.Face` — Type

A `Face` is a collection of graphical attributes for displaying text. Faces control how text is displayed in the terminal, and possibly other places too.

Most of the time, a `Face` will be stored in the global faces dicts as a unique association with a face name Symbol, and will be most often referred to by this name instead of the `Face` object itself.

Attributes

All attributes can be set via the keyword constructor, and default to `nothing`.

- `height` (an `Int` or `Float64`): The height in either deci-pt (when an `Int`), or as a factor of the base size (when a `Float64`).
- `weight` (a `Symbol`): One of the symbols (from faintest to densest) `:thin`, `:extralight`, `:light`, `:semilight`, `:normal`, `:medium`, `:semibold`, `:bold`, `:extrabold`, or `:black`. In terminals any weight greater than `:normal` is displayed as bold, and in terminals that support variable-brightness text, any weight less than `:normal` is displayed as faint.
- `slant` (a `Symbol`): One of the symbols `:italic`, `:oblique`, or `:normal`.
- `foreground` (a `SimpleColor`): The text foreground color.
- `background` (a `SimpleColor`): The text background color.
- `underline`, the text underline, which takes one of the following forms:
  - a `Bool`: Whether the text should be underlined or not.
  - a `SimpleColor`: The text should be underlined with this color.
  - a `Tuple{Nothing, Symbol}`: The text should be underlined using the style set by the Symbol, one of `:straight`, `:double`, `:curly`, `:dotted`, or `:dashed`.
  - a `Tuple{SimpleColor, Symbol}`: The text should be underlined in the specified SimpleColor, and using the style specified by the Symbol, as before.
- `strikethrough` (a `Bool`): Whether the text should be struck through.
- `inverse` (a `Bool`): Whether the foreground and background colors should be inverted.
- `inherit` (a `Vector{Symbol}`): Names of faces to inherit from, with earlier faces taking priority. All faces inherit from the `:default` face.

source
`StyledStrings.addface!` — Function

    addface!(name::Symbol => default::Face)

Create a new face by the name `name`. So long as no face already exists by this name, `default` is added to both `FACES``.default` and (a copy of) to `FACES`.`current`, with the current value returned.

Should the face `name` already exist, `nothing` is returned.

Examples

    julia> addface!(:mypkg_myface => Face(slant=:italic, underline=true))
    Face (sample)
             slant: italic
         underline: true

source
`StyledStrings.withfaces` — Function

    withfaces(f, kv::Pair...)
    withfaces(f, kvpair_itr)

Execute `f` with `FACES``.current` temporarily modified by zero or more `:name => val` arguments `kv`, or `kvpair_itr` which produces `kv`-form values.

`withfaces` is generally used via the `withfaces(kv...) do ... end` syntax. A value of `nothing` can be used to temporarily unset a face (if it has been set). When `withfaces` returns, the original `FACES``.current` has been restored.

Examples

    julia> withfaces(:yellow => Face(foreground=:red), :green => :blue) do
               println(styled"{yellow:red} and {green:blue} mixed make {magenta:purple}")
           end
    red and blue mixed make purple

source
`StyledStrings.SimpleColor` — Type

    struct SimpleColor

A basic representation of a color, intended for string styling purposes. It can either contain a named color (like `:red`), or an `RGBTuple` which is a NamedTuple specifying an `r`, `g`, `b` color with a bit-depth of 8.

Constructors

    SimpleColor(name::Symbol)  # e.g. :red
    SimpleColor(rgb::RGBTuple) # e.g. (r=1, b=2, g=3)
    SimpleColor(r::Integer, b::Integer, b::Integer)
    SimpleColor(rgb::UInt32)   # e.g. 0x123456

Also see `tryparse(SimpleColor, rgb::String)`.

source
`Base.parse` — Method

    parse(::Type{SimpleColor}, rgb::String)

An analogue of `tryparse(SimpleColor, rgb::String)` (which see), that raises an error instead of returning `nothing`.

source
`Base.tryparse` — Method

    tryparse(::Type{SimpleColor}, rgb::String)

Attempt to parse `rgb` as a `SimpleColor`. If `rgb` starts with `#` and has a length of 7, it is converted into a `RGBTuple`-backed `SimpleColor`. If `rgb` starts with `a`-`z`, `rgb` is interpreted as a color name and converted to a `Symbol`-backed `SimpleColor`.

Otherwise, `nothing` is returned.

Examples

    julia> tryparse(SimpleColor, "blue")
    SimpleColor(blue)

    julia> tryparse(SimpleColor, "#9558b2")
    SimpleColor(#9558b2)

    julia> tryparse(SimpleColor, "#nocolor")

source
`Base.merge` — Method

    merge(initial::StyledStrings.Face, others::StyledStrings.Face...)

Merge the properties of the `initial` face and `others`, with later faces taking priority.

This is used to combine the styles of multiple faces, and to resolve inheritance.

source

Theme

This document was generated with Documenter.jl version 1.17.0 on Thursday 9 April 2026. Using Julia version 1.12.6.