#markup-language #config-file #markup #language #file-format #sml #simple


A Rust implementation of a parser/writer for the Simple Markup Language format, as defined by Stenway. See https://dev.stenway.com/SML/. SML builds on top of WSV but allows hierarchical structuring of data.

7 releases (2 stable)

1.0.1 Apr 10, 2024
1.0.0 Apr 7, 2024
0.3.0 Mar 17, 2024
0.2.2 Feb 3, 2024
0.1.0 Jan 27, 2024

#9 in #markup-language

23 downloads per month
Used in simpleml_macro

MIT license

859 lines


This crate is a rust implementation of the Simple Markup Language specification. This specification is built on top of the Whitespace Separated Value specification and provides a human-friendly configuration file format.

Patch Notes


Updating the dependency on whitespacesv from 1.0.1 to 1.0.2, which fixes a panic when writing jagged arrays. Since SML is built on top of WSV, this impacted the SMLWriter as well.


This crate is 1.0 now! No breaking changes were introduced in this version, but it fixes a bug where malformed SML like the following would cause a panic:

    # No closing tag


This crate only provides a two APIs for parsing SML files. The parse and parse_owned functions will parse the SML input, returning a Result. The Ok variant is a TreeNode from the tree_iterators_rs crate representing the elements of the hierarchy. I have chosen to build on top of it to provide you with all of the tree traversal utility methods built there when working with your SML content. I recommend adding use tree_iterators_rs::prelude::*; to the files that handle the SML content to pull the traversal methods into scope. The only difference between the two APIs is that parse uses Cow<'_, str>'s to represent the SML nodes, and parse_owned uses Strings to represent the SML nodes. If you don't want to deal with lifetimes, use parse_owned.

Because SML is an extension on top of WSV, I have also pulled in whitespacesv as a dependency.

In-line Declaration

If you plan to include any SimpleML in your rust code or build system, consider using simpleml_macro to maintain everything in valid SML format.


In order to write an SML file, use the SMLWriter struct. It provides several configuration options, including:

  1. any custom end keyword
  2. the column alignment of SML attribute WSV tables
  3. the indentation string (this must be whitespace)

The list of whitespace characters is defined as follows:

Codepoint 	Name
U+0009 	    Character Tabulation
U+000A 	    Line Feed
U+000B 	    Line Tabulation
U+000C 	    Form Feed
U+000D 	    Carriage Return
U+0020 	    Space
U+0085 	    Next Line
U+00A0 	    No-Break Space
U+1680 	    Ogham Space Mark
U+2000 	    En Quad
U+2001 	    Em Quad
U+2002 	    En Space
U+2003 	    Em Space
U+2004 	    Three-Per-Em Space
U+2005 	    Four-Per-Em Space
U+2006 	    Six-Per-Em Space
U+2007 	    Figure Space
U+2008 	    Punctuation Space
U+2009 	    Thin Space
U+200A 	    Hair Space
U+2028 	    Line Separator
U+2029 	    Paragraph Separator
U+202F 	    Narrow No-Break Space
U+205F 	    Medium Mathematical Space
U+3000 	    Ideographic Space

An example of how to use the SMLWriter is as follows:

use tree_iterators_rs::prelude::*;
use simpleml::{SMLWriter, SMLElement, SMLAttribute};

// Build up our value set
let my_sml_values = TreeNode {
    value: SMLElement {
        name: "Configuration",
        attributes: Vec::with_capacity(0),
    children: Some(vec![
        TreeNode {
            value: SMLElement {
                name: "Video",
                attributes: vec![
                    SMLAttribute {
                        name: "Resolution",
                        values: vec![Some("1280"), Some("720")],
                    SMLAttribute {
                        name: "RefreshRate",
                        values: vec![Some("60")],
                    SMLAttribute {
                        name: "Fullscreen",
                        values: vec![Some("true")],
            children: None,
        TreeNode {
            value: SMLElement {
                name: "Audio",
                attributes: vec![
                    SMLAttribute {
                        name: "Volume",
                        values: vec![Some("100")],
                    SMLAttribute {
                        name: "Music",
                        values: vec![Some("80")],
            children: None,
        TreeNode {
            value: SMLElement {
                name: "Player",
                attributes: vec![SMLAttribute {
                    name: "Name",
                    values: vec![Some("Hero 123")],
            children: None,

// actually write the values
let str = SMLWriter::new(my_sml_values)
    // Setting up a custom end keyword
    // Using 8 spaces as the indent string. The default is 4 spaces.
    .indent_with("        ")
    // Align the WSV tables to the right.

/// Result:
/// Configuration
///         Video
///                  Resolution 1280 720
///                 RefreshRate   60
///                  Fullscreen true
///         my_custom_end_keyword
///         Audio
///                 Volume 100
///                  Music  80
///         my_custom_end_keyword
///         Player
///                 Name "Hero 123"
///         my_custom_end_keyword
/// my_custom_end_keyword
println!("{}", str);


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