Case conventions on element names?

Question

Are there any formal recommendations on element casing in XML?

I know XHTML uses lowercase element names (as opposed to HTML which canonically uses uppercas

Answer 1

To add to Metro Smurf's answer.

The National Information Exchange Model (NIEM: http://en.wikipedia.org/wiki/National_Information_Exchange_Model) says to use:

• Upper CamelCase (PascalCase) for elements.
• (lower) camelCase for attributes.

The NIEM makes for a good option when you're looking to conform to some standard.

Answer 2

I wouldn't say HTML "canonically" uses uppercase. I think originally uppercase was used to visually separate HTML from the content more easily. With syntax highlighting nowadays, that's just not necessary.

I veer towards lowercase, with dashes if necessary (quicker to type, too). Mixing case in XML just feels wrong to me.

Answer 3

There is no formal recommendation.

Since XML was designed with the twin purposes of holding documents and exchanging information between disparate systems, it was designed so as to be able to match the applications using it.

So .Net XML tends to use ProperCasing (witness XAML), while other XML will use camelCasing, python_conventions, dot.naming, and even COBOL-CONVENTIONS. The W3C seems to like lower-case-with-dashes-quite-a-bit (e.g. XSLT) or justlowercasewordssmashedtogether (e.g. MathML).

I like all lower case and no underscores, since that means less use of the [Shift] key, and my fingers are a little lazy. :)

Answer 4

See the UN/CEFACT XML Naming and Design Rules Technical Specification Version 3.0 page 23 for some example rules used in several standards.

Specifics (from page 23 of Version 3.0 dated 17 December 2009):

• LowerCamelCase (LCC) MUST be used for naming attributes.
• UpperCamelCase (UCC) MUST be used for naming elements and types.
• Element, attribute and type names MUST be in singular form unless the concept itself is plural.

(other link, Swedish site)

Answer 5

Camel case gets my vote.

As to cited examples perhaps this question can be come the link people cite.

Answer 6

Most XML standards originating from the W3C tend to use lower case with hyphens.

There is a philosophical distinction between seeing XML as a format for platform neutral documents, which W3C standards try to encourage, and languages such as XAML which see XML as a serialisation of a platform specific object graph.

If you're not using XML as a platform neutral document format, but as an application specific serialisation, then you might as well save yourself some bother and have a 1:1 correspondence between the XML names and the platform specific names. But almost any other object graph format is better than XML for that purpose.

If you are, then you might want to fit in with XHTML, XSLT, SVG, XProc, RelaxNG and the rest.