Namespace node replacement - pluggable filters

[lukevenediger]

Namespaces can contain placeholders that will be replaced with an actual value, using a pluggable filter.

For example, foo.bar.{geo(city,45.2314,98.23145)}.baz - will invoke the geo plugin to extract the city name based on a latitude and longitude reading. Other plugin examples could be:

• IP address geolocation
• Acronym expansion
• significant day replacement (e.g holiday names)

The plugin must replace a whole node, and will return one or more nodes.

The format for a plugin is:
{ plugin_name ( arg0, arg1 .. argN ) }

A plugin with zero arguments does not require parentheses:
{ plugin_name }