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Contributor Guide

This guide is for developers who want to contribute code to MathLive, or who want to understand in more depth how MathLive works. If you simply want to use MathLive with your web content, see the Usage Guide.

Table of Contents

Getting Started: Setting up Your Development Environment

The project uses NPM scripts for its build system. The package.json file contains the definitions of the build scripts.

To get started developing:

  1. Install Node.js on your dev machine
  2. In your shell, type:
    $ git clone https://github.com/arnog/mathlive && cd mathlive
    $ npm install
    The npm install command installs in the mathlive/ directory all the Node modules necessary to build and test the MathLive library and its documentation.

Depending on your system setup, you may need to run as admin, in which case use sudo npm install.

Once the installation is successful, you can use the following commands:

# Build the project for local use
# 1. Compile the `.css/.less` file to `build/*.css`
# 2. "npm run lint" on the .js files
# 3. "npm run docs" to generate the documentation
$ npm run build

# Auto re-build the project when a file changes.
# Watch for changed files, and does "npm run build" and "npm run test"
$ npm run dev

# Run test scripts
$ npm test

# Lint Javascript files
$ npm run lint

# Calculate the code coverage and output to build/coverage/
$ npm run coverage

# Build the documentation file to `docs/`
$ npm run docs

# Clean up (deletes) the contents of the `build/`, `dist/` and `docs/` directories
$ npm run clean

# Clean, build, then transpile, minimize and bundle to `dist/`.
# The `dist/` folder will contain the `.js`, `.css` and font files necessary to 
# use MathLive. The `docs/` folder will also be updated.
$ npm run dist

During development, it is recommended that you keep the npm run dev command running in a terminal window while you make the necessary changes to the source files of the project in your favorite editor. When you save a file, if any problem with your code is detected (linting failure, unit test failure), it will be displayed in the terminal window.

Before doing a commit to master it is also recommended that you do a npm run dist to make sure that the content of the dist/ and docs/ directory are in sync with your latest changes.

After you push your changes to master, a Travis continuous integration task will run npm run dist and npm run test. If either of those tasks fail, the build will be marked as failed and will need immediate fixing.

Publishing

Once you have made significant changes that are ready to be shared broadly, use the following commands:

# Increase the version number of the library
# Only do this before making a new public distribution
# After doing this, you can `npm publish`
$ npm version major | minor | patch |

# Do a full build (code, docs, test), then publish the package to npmjs.com
$ npm publish

Note on versioning Use the semver convention for versions:

  • npm version patch: bug fixes and other minor changes. Last number of the version is incremented, e.g. 1.2.411.2.42
  • npm version minor: new features which don't break existing features. Middle number of the version is incremented, e.g. 1.2.421.3.0
  • npm version major: changes which break backward compatibility of the API. Increment the first number, e.g. 1.3.562.0.0

Code Structure

The MathLive library consists of the following key directories:

  • css/ the stylesheets and fonts used by MathLive
  • src/core the core Javascript code needed to render math. This module depends on the css/ module.
  • src/editor the Javascript code needed for the editor. This module depends on the src/core module.
  • src/addons some optional modules that provide additional functionality

You can include only the files you need. For example, if you only need to display math, you can skip src/editor/ and src/addons.

In addition, the build/ and dist/ directories contain optimized output generated from the css/ and src/ directories:

  • the build/ directory contains intermediary build results. These intermediary results can be used for debugging during development, but are not suitable for distribution. For example, this directory will contain the .css files generated from the .less in css/. However, a transpiled or minified .js file would not, as those are intended for distribution and should be in the dist/ directory.
  • the dist/ directory contains the build results that are ready for distribution. The files in this directory should be transpiled (for .js files), autoprefixed (for .css files), minimized and bundled.
  • finally, the docs/ directory contain documentation generated from the source code.

The content of the build/, dist/ and docs/ directories are entirely generated as part of the build process. No other directory should contain intermediated files generated as part of the build process.

Language and Coding Style

MathLive is written in Javascript, using the ES2016 dialect. This includes in particular these features:

  • let and const instead of var
  • block-scoped variables and functions
  • Array.prototype.includes()
  • Object.assign()
  • arrow functions (to a limited extent, there appears to be issues with transpilers)
  • template strings
  • for...of iterators
  • string searching String.startsWith(), String.endsWith()
  • number formatting

Features that have not been adopted include:

  • classes. The syntax doesn't seem to offer that much benefit and forces utility functions to be separated from methods that use them.
  • getters/setters: would probably be a good idea
  • destructuring: probably some opportunities to simplify some code
  • default parameters: would clean up some code
  • rest/spread
  • generators

Before publishing, Babel transpiles the code so it can run on recent browsers, even if they don't support all the ES2016 features yet. The code is also optimized for performance and minimized to reduce the load time.

The code base attempts to follow these general guidelines:

  • Consistency All code in the codebase should look as if it had been written by a single person. Don't write code for yourself, but for the many people who will read it later.
  • Clarity before performance Write code that is easy to read, and avoid obscure constructs that may obfuscate the code to improve performance. For example, RegEx are crazy fast in all modern browsers, and trying to roll out your own pattern matching will result in more code and less performance. If you think something could be made faster, use jsperf.com to try out options in various browsers and compare the results. You might be surprised.
  • Follow Postel's Law, the Robustness Principle "Be conservative in what you do, be liberal in what you accept from others". For example, functions that are invoked internally do not need to check that the input parameters are valid. However, public APIs should check the validity of parameters, and behave reasonably when they aren't.

Use the .eslintrc.json file to follow the linting conventions used in the project. In addition, follow these guidelines:

  • Tabs are expanded to four spaces
  • Quotes are preferably single quotes. Use double-quotes when inside a single-quoted string. Using backtick (template strings)for multiline quotes is OK.
      let s = 'hello, ' + 'world';
      s = 'hello, "world"';
      s = `hello:
    world`;
  • Typecheck using typeof v === 'string', typeof v === 'number', etc... Use Array.isArray(v) to check for arrays.
  • Conditional evaluation. Use conditional evaluation shortcuts when applicable for example, use if (string) instead of if (string !== '')
  • The variable holding the return value of a function is usually named result
  • Avoid boolean as arguments. Instead, use an options object with key/value pairs spelling out the meaning of the boolean. Don't do:
      f(true);
    Do:
      f({reverse: true})
  • Use || for default values. For example
      m = f(n) || d;
    If the function f returns null, undefined or an empty string, m will have the value d
  • Braces for control structures should always be used, except for short if statement, for example if (done) return;
  • Avoid method chaining. Method chaining is a programming style where a method returns the this object so that it can be called again. For example div.css('color', 'white').height(50).width(50).
  • Use loose typing. For example, a function argument could accept a string or an array and behave appropriately:
      function f(argument) {
          if (Array.isArray(argument)) {
              argument = argument.join(';');
          }
      }

Naming Conventions

Those naming conventions are particularly important for objects that are exposed as part of the public API, such as MathLive and MathField.

  • variables and function names that begin with _ are private and should not be used.
  • functions that end in _ are selectors and should not be invoked directly. Instead, a MathField.perform() call should be made. Note that the perform call does not include the _, so you would call MathField.perform('selectAll').
  • functions that neither begin nor end with an _ are public and can be called directly.

Browser Support

MathLive is designed for the modern web. Supporting older browsers complicates the effort involved in building new features, but it is also an insecure practice that should not be encouraged.

In this context, modern means the latest two releases of Chrome, IE, Safari and Firefox. Both desktop and mobile are supported.

Accessibility - A11Y

Rendering

MathLive renders math using HTML and CSS. Digits, letters and math symbols are displayed in <span> tags with the necessary CSS styling to display them in the right place. In addition, rules (lines) such as the fraction line, are rendered using CSS borders. In a few rare cases, SVG is used to render some decorations, such as the annotations of the \enclose command.

The rendered math is not purely graphical, and as such can be accessed by screen readers.

Alternate renditions

However, in addition to the "visual" HTML+CSS representation that MathLive outputs, it can also generate alternate renditions, including:

  • LaTeX: a string of LaTeX code equivalent to the formula.
  • Spoken Text: a text representation of the formula as someone would speak it, for example: f(x) = x^2 → "f of x equals x squared"
  • Annotated Spoken Text: as above, but in addition prosody hints are inserted for a more natural rendition by text to speech systems (breathing pauses, variation in pitch, etc...).

Those alternate renditions can be rendered as an ARIA-label, or as an element that is not visually rendered, but visible to screen readers.

Speech

Although MathLive works with screen readers, since math is its own language MathLive has its own built-in text to speech renderer. With the speech interface it is possible to:

  • read the current group (numerator or subscript, for example)
    • Mac: Ctrl + Command + Down
    • Windows/Linux/ChromeOS: Ctrl + Alt + Down
  • read what's before or after the selection
    • Mac: Ctrl + Command + Left/Right
    • Windows/Linux/ChromeOS: Ctrl + Alt + Left/Right
  • read the parent of the current group
    • Mac: Ctrl + Command + Up
    • Windows/Linux/ChromeOS: Ctrl + Alt + Up
  • read the current selection
    • Mac: Ctrl + Command + Shift + Down
    • Windows/Linux/ChromeOS: Ctrl + Alt + Shift + Down

With these convenient keyboard shortcuts, it is possible to aurally navigate and understand even complex formulas.

Input and navigation

MathLive supports multiple modalities for input: in addition to pointer devices (mouse, trackpad, touch screen), MathLive has an extensive set of keyboard shortcuts that allow navigation and editing of the most complex formulas. Every operation is possible without the use of a pointing device.

Conversely, it is possible to enter commands and complex mathematical symbols using only a pointing device: the command bar can be invoked by tapping a round toggle button displayed to the right of the formula. The command bar offers large buttons that act as a virtual keyboard, but offer contextual operations depending on the current selection, and the content around it. Those buttons are easy to use on touch screens and for users of alternative pointing devices.

Architecture

The core of MathLive is a math rendering engine that can output to HTML and CSS. This engine uses the TeX layout algorithms because of their quality. Given the same input, MathLive will render pixel for pixel what TeX would have rendered. To do so, it makes use of a web version of the fonts used by TeX and which are included in the dist/fonts/ directory. Although the rendering engine follows the TeX algorithms, MathLive also has an in-memory data structure to represent a math expression while it is being edited (the math atom tree).

Here are some of the key concepts used throughout the code base.

Span

A span is an object that is used to represent an element displayed in a web page: a symbol such as x or =, an open brace, a line separating the numerator and denominator of a fraction, etc...

The basic layout strategy is to calculate the vertical placement of the spans and position them accordingly, while letting the HTML rendering engine position and display the horizontal items. When horizontal adjustments need to be made, such as additional space between items the CSS margin are adjusted.

Spans can be rendered to HTML markup with Span.toMarkup() before being displayed on the page.

Math Atom

An atom is an object encapsulating an elementary mathematical unit, independent of its graphical representation.

It can be of one of the following types:

  • ord: ordinary symbol, e.g. x, \alpha
  • bin: binary operator: +, *, etc...
  • rel: relational operator: =, \ne, etc...
  • punct: punctuation: ,, :, etc...
  • open: opening fence: (, \langle, etc...
  • close: closing fence: ), \rangle, etc...
  • op: (big) operators, \sum, \cap.
  • inner: special layout cases, overlap
  • accent: a diacritic mark above a symbol

In addition to these basic types, which correspond to the TeX atom types, some atoms represent more complex compounds, including:

  • space and spacing: blank space between atoms
  • mathstyle: to change the math style used: display or text. The layout rules are different for each, the latter being more compact and intended to be incorporated with surrounding non-math text.
  • font: to change the font used. Used by \mathbb, \mathbb, etc...
  • sizing: to change the size of the font used
  • color: to change the foreground color
  • rule: a line, for the \rule command
  • line: used by \overline and \underline commands
  • box: to draw a border around an expression and change its background color
  • overlap: display a symbol over another
  • overunder: displays an annotation above or below a symbol
  • group: a simple group of atoms
  • root: a group, which has no parent
  • array: a group, which has children arranged in columns and rows. Used by environments such as matrix, cases, etc...
  • genfrac: a generalized fraction: a numerator and denominator, separated by an optional line, and surrounded by optional fences
  • surd: a surd, aka root
  • leftright: used by the \left and \right commands
  • delim: some delimiter
  • sizeddelim: a delimiter that can grow

The following types are used by the editor:

  • command indicate a command being entered. The text is displayed in blue in the editor.
  • error: indicate a command that is unknown, for example \xyzy. The text is displayed with a dotted red underline in the editor.
  • placeholder: indicate a temporary item. Placeholders are displayed with a a pill (rounded box) in the editor.
  • first: a special, empty, atom put as the first atom in math lists in order to more easily represent the cursor position. They are not displayed.

Math List

A math list is simply an array of atoms. Although it's a common data structure there is no class to represent it: it's simply an Array of MathAtom objects.

Lexer

The lexer converts a string of TeX code into tokens that can be digested by the parser.

Parser

The parser turns a stream of tokens generated by the lexer into math atoms. Those atoms then can be rendered into spans, or back into LaTeX or into spoken text.

Editable Math List

An Editable Math List is a class specific to the editor. It encapsulates the operations that can be done to an editable math list, including adding and removing content and keeping track of and modifying an insertion point and selection.

Math Field

A MathField is a user interface widget that captures the keyboard and pointing device events, and present an appropriate user experience. It uses the EditableMathList to manipulate the in-memory representation of the math expression being edited.

Files

Here's a brief guide to the files of the project:

  • mathlive.js The public API to Mathlive

  • core/lexer.js Implements the Lexer class: strings to tokens

  • core/parser.js Implements the Parser class: tokens to atoms

  • core/definitions.js Dictionary of all the known LaTeX commands, and which symbol or atom type they map to. Used by the Parser
  • core/color.js Support to parse color arguments

  • core/mathAtom.js Implements the MathAtom class: atoms to spans

  • core.delimiters.js Rendering (atoms to span) for delimiters.
  • core/context.js Rendering context of the current parse level (math style, color, font size, font family, font style, etc...). Used by MathAtom while generating spans
  • core/mathstyle.js Provides info about the math styles: display, text, scripttext, scripscripttext and their tight variants.
  • core/fontMetrics.js Provides glyph metrics: height above baseline, depth below baseline, italic correction.
  • core/fontMetricsData.js Used by fontMetrics.js

  • core/span.js Implements the Span class: spans to markup

  • editor/editableMathlist.js: The EditableMathlist keeps track of a tree of math atoms representing the math expression being edited, and a selection with can either be collapsed (only the insertion point is visible) or not, in which case it has an extent indicating how big the selection is. This class has no UI logic in it.

  • editor/mathpath.js A utility class that represents a path in an atom tree to a specific atom

  • editor/mathfield.js Public API for the editor. Implements the UI for the mathfield, including mouse and touch interaction, and the popover and the command bar

  • editor/shortcuts.js Defines the keyboard shortcuts
  • editor/commands.js: list of commands displayed in the command bar
  • editor/popover.js Implements the popover panel
  • editor/keyboard.js A utility class that captures keyboard events from a Textarea DOM element.
  • editor/undo.js Implements the Undo Manager which keeps tracks of the state of the mathfield as it is being edited in order to support undo/redo.

Common Tasks

So, you want to...

Add a new LaTeX command?

(1) Start with core/definitions.js. Add a new entry to the appropriate table by calling defineSymbol() for commands that need to parameters, defineFunction() for commands that need some parameters or defineEnvironment() for environments, complex \begin{}...\end{} block.

For functions, the handler function in the definition will be called by the parser at the right time. It's your chance to store data that will be used by the atoms to render the symbol later.

(2) If you can use the existing atom types, great. If needed, modify an existing atom type to support what you want, including passing additional parameters. If no atom types match, create a new one by adding a new MathAtom.decompose<atom-type>() function and calling it from MathAtom.decompose().

(3) Call makeSpan() and its variants in your decompose function to construct a representation of the atom.