HTML5: example of chemical identifier annotation

The chemid vocabulary defined at can be used to annotate a selected HTML element containing information on a chemical species. This requires two markup/annotation steps:

1. Selection of an HTML element. Select the HTML element of interest and include the two attributes itemscope and itemtype into its start tag. The HTML5 specification does not require a value for itemscope, but for XML compatibility you may want to use the assignment itemscope="itemscope". The itemtype attribute provides the URL for the vocabularity—in our case, the chemid vocabulary link given above.

2. Insertion of child elements. Any vocabulary-defined property can then be incorporated into the selected element via child elements, for example, by using the em, span and code tags. These child elements are upgraded as microdata by including an itemprop attribute in their start tag, the value of which is a valid property from the vocabulary.
The following example illustrates the annotation of a text snippet reporting on some use of the chemical compound dimethyl carbonate. In addition to the annotation of the compound name itself by CompName, an acronym, the molecular formula and the CAS registry number are supplied, specified via attribute values ShortName, FormulaSub and CASRN, respectively.
<div itemscope="itemscope"
..As reaction medium we are employing a green solvent:
..<em itemprop="CompName">dimethyl carbonate</em>
..(<span itemprop="ShortName">DMC</span>,
...<code itemprop="FormulaSub"> .....C<sub>3</sub>H<sub>6</sub>O<sub>3</sub>
...<span itemprop="CASRN">616-38-6</span>).
..Notice that this reagent has a flash point in
..the room temperature range.
The W3C Markup Validator at may report errors while evaluating HTML5 pages with microdata markup: for various element types, the validator does not accept the itemprop attribute “at this point.” We experienced good validation performances with the (X)HTML5 Validator at

Vocabulary author: Axel Drefahl
Last update: December 19, 2014
Axel at ResearchGate

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