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A template engine for HTML

Razor Leaf is a template engine for JavaScript with a convenient indentation-based syntax. It aims to reduce the redundancy inherent in HTML with simple rules, a sparse syntax, and a few further features not found in larger libraries.

Elements are defined by their names only; no other special character is necessary.


Void elements are recognized automatically.


Strings are double-quoted and escaped for use in HTML as needed. Backslash escape codes can be used as in JavaScript. No whitespace is added around strings.

"--> A string <--\n" "A string containing \"double-quotes\""
--&gt; A string &lt;--
A string containing "double-quotes"

Strings can also contain interpolated sections, delimited by #{ and }. #{ can be escaped with a leading backslash; } doesn’t require escaping.

"#{6 * 7}"

If an exclamation mark precedes the string, it and any of its interpolated sections will not be escaped.

!"<!-- A significant comment -->"
<!-- A significant comment -->

Attributes are marked up using the syntax name:. An attribute name can, optionally, be followed by a string to be used as its value; if a value isn’t provided, the attribute is assumed to be boolean (and present). Note that a string used as an attribute’s value cannot be “raw” — that is, cannot be preceded by an exclamation mark.

meta charset: "utf-8"
<meta charset="utf-8">

Classes are marked up with a leading period, as in .class.

fieldset .upload-meta
<fieldset class="upload-meta"><input class="required"></fieldset>

Hierarchy in Razor Leaf is defined using indentation. For example:

        meta charset: "utf-8"
        title "Example"
            rel: "stylesheet"
            type: "text/css"
            href: "stylesheets/example.css"
        p id: "introduction"
            "This template is a brief example of hierarchy."
<!DOCTYPE html><html><head><meta charset="utf-8"><title>Example</title><link rel="stylesheet" type="text/css" href="stylesheets/example.css"></head><body><p id="introduction">This template is a brief example of hierarchy.</p></body></html>

Content found after an element on the same line will also be considered that element’s content.

Comments begin with # and continue to the end of the line. They do not affect the rendered HTML.

Code blocks begin with % and continue to the end of the line. Code blocks may contain content (strings, elements, other code blocks, and special blocks, but not attributes); if they do, they are treated as blocks and wrapped in curly braces.

For example, this template:

% function countTo(n)
    % for (var i = 1; i <= n; i++)
% countTo(5);

might compile to this JavaScript:

function countTo(n) {
    for (var i = 1; i <= n; i++) {
        output += i;

Some names define special blocks. These are:

  • doctype: Inserts <!DOCTYPE html>.
  • if (condition): Includes its content only if condition is met.
  • elif (condition): Can immediately follow an if or an elif.
  • else: Can immediately follow an if or an elif.
  • for (identifier) of (collection): Includes its content for each element of the array or array-like object collection.
  • for (identifier), (index) of (collection): Allows the index variable in a for loop to be named.
  • include (name): Loads and includes another template.
  • extends (name): Loads another template and replaces its blocks. A template that extends another template cannot have any content outside of block actions.
  • block (name): Defines a replaceable block.
  • replace (name): Replaces a block.
  • append (name): Appends to a block.

Creates a loader that maps template names to files with the .rl extension in the directory located at root.

Returns a template object loaded from the root directory.

Compiles a template string into a function. The compiled function takes one argument, data, which can be used (under that name) in the template.

  • debug: If true, warnings will be printed. (In a later version, this will enable error rewriting.)
  • load(name): A function that returns a parsed template represented by name. This is filled automatically by most loaders.
  • globals: An object representing the global variables that should be made available to the template.