| Genus name | Species name | commonly |
| Homo | sapiens | human |
| Picea | glauca | white spruce |
| Agoseris | glauca | prairie agoseris |
| Pilosocereus | leucocephalus | a fuzzy cactus with a pretty pink/red flower |
| Haliaeetus | leucocephalus | bald eagle |
| TEI | <head> |
a heading, e.g. of a chapter |
| HTML | <head> |
container for metadata |
| TEI | <constraint> |
a formal constraint (e.g., in ISO Schematron) not expressed in the structural content model |
| DocBook | <constraint> |
a constraint in an EBNF production |
When you look at an element (for instance in TEI), you see its name: every element has a name (e.g. div or p). What may be less obvious is that this name is only part of its full, formal designation. What we’re seeing when we look at an XML element, typically, is like a species name (for instance, glauca). We can see from these examples that many creatures may have the same species name: what makes the name unique is the combination of the genus and species names.
In a very similar way, XML elements have both genus and species names. In the example here, we’re only seeing the species name, and in fact we can’t tell by looking at this slide what the real element names are: we don’t know what language they’re in (TEI? HTML?) In order to know what language an element is in, we need both. That’s where namespaces come in.
