Describe how XML namespace support works

[jclark]

The spec describes the syntax for describing an XML namespace, but we don't completely describe the effect that this is supposed to have. If we have a xmlns decl for a prefix p as namespace uri, then in certain situations a qualified identifier p:ident is supposed to turn into an expanded name {uri}ident.

This is an important point, because it was part of the motivation for using prefix:name as the qualified identifier syntax.

Relates to #85.

[jclark]

Need to think about where we have imported a module as foo, but still want to be able to use foo as an XML namespace prefix. A special case of this is xml where it is natural to want to import the lang.xml module as xml but we also need to use the xml as a namespace prefix.

[jclark]

Things that need to be said:

• [done] xml import prefix predeclared and overrideable
• [done] xml:space etc included in lang.xml
• [done] xmlns namespace prefix predeclared and not overrideable
• [done] which namespace attributes are added when constructing from xml infoset
• [done] namespace attribute handling on serialization
• [done] foo:bar works as string, if foo is a namespace prefix (do we need this if we have x.foo:bar = "baz"?)

[rdhananjaya]

Could you please elaborate on second point xmlns:space etc included in lang.xml a bit.

[jclark]

I meant xml:space. The idea is that lang.xml does:

const space = "{http://www.w3.org/XML/1998/namespace}space";

This is so you can say:

xml:Element e;
map<string> atts = e.getAttributes();
string? s = atts[xml:space];

Thus the xml prefix (which is a module prefix) will work like prefixes that are defined as namespace prefixes.

It should also work for . and ?. e.g.

xml:Element e;
string? s = e?.xml:space;

but the spec doesn't cover this yet.