CSC/ECE 517 Fall 2017/M1752 Implement the Microdata API

M1752 : Implement the Microdata API

Introduction

Scope

The scope of this project is to implement initial support for Microdata API specification by allowing the Servo engine to read Microdata API tags from web pages and interpret them in the DOM. This should lay a groundwork for future improvements to implement features to created vCard and JSON data from Microdata on the ServoShell. Additional project information is available here

Specification

The WHATWG Microdata HTML specification allows web data to be enriched in that it allows machines to learn more about the data in a web page. A typical example of an HTML file with Microdata is shown below -

This specification consists of the following HTML attributes. Out of which ‘itemtype’ and ‘itemprop’ are currently in scope.

More information about the Microdata specification is available here

Some popular websites like Google, Skype and Microsoft use the Microdata. The number of websites that use Microdata is growing; currently about 13% of websites use Microdata (statistics courtesy Alexa)

Design

As for the initial stage of this project, the scope did not require any major changes to the engine design. We implemented a DOM method to handle appropriate attributes in the Microdata API. The below diagram shows an overview of components involved in the design. The highlighted blocks have been modified.

Implementation

The implementation involved updates to the Web Interface Definition Language (webidl) files and its Rust implementation.

HTMLElement.WebIDL

Method Name	Return Type	Description
propertyNames()	String	Method definition only. The implementation is done in htmlelement.rs

htmlelement.rs

Method Name	Return Type	Description	Location
parse_plain_attributes()	AttrValue	This method returns a value of an attribute associated to an the HTML Element.	traits Virtual_Methods
propertyNames()	Option<Vec<DOMString>>	This method parses the space-separated values of the 'item-type' attributes'	struct HTMLElement

Configuration

The preference [Pref="dom.microdata.testing.enabled"] was added to toggle the experimental microdata methods during development.

Testing

testharness is used as the testing framework.

Dependencies

html5ever - HTML attribute names are fetched in Servo from a lookup file in the html5ever module. The html5ever module was augmented with the 'itemprop' and 'itemtype' attributes for use in Servo.

Pull Request

The pull request used to incorporate our changes upstream is available here

References

http://html5doctor.com/microdata/