One of the ways in which code is structured in large applications involves namespacing (the practice of dividing code up by naming identifiers). One namespace could contain everything relating to Ajax, whereas another could contain classes related to mathematics. Programming languages (such as C# and Java) even incorporate namespaces as a first-class language construct to help with code organization.

Separating code from directories based on namespace becomes a sensible extension of this:

From left: Java's Platform API, Ext JS 5, and .NET Framework

A namespace identifier is made up of one or more name tokens, such as "Java" or "Ext", "Ajax" or "Math", separated by a symbol, in most cases a full stop/period. The top level name will be an overarching identifier for the whole package (such as "Ext") and will become less specific as names are added and you drill down into the code base.

The Ext JS source code makes heavy use of this practice to partition UI components, utility...