In section 2.2, the following appears:

Only a root object is obtained from the injector.... This object is generally the entry
point of an application and is typically requested only once. ... no
matter how many client-service systems exist within the application, their creation,
injection, and usage cascades from the root object. ....


I am lost as to the meaning of this.

Is the Emailer somehow the "root object" you're talking about? It's hard to see how the rest of the paragraph could apply to the Emailer, but in your example, what's obtained from the injector is, well, an Emailer.


I am confused about what it means for "client-service systems..usage" to "cascade from the root object". What does it mean for a usage to cascade from an object? To cascade at all?