StringSink Documentation Clarification

[RohitSaily]

The StringSink documentation does not specify if implementations can overwrite on writes. I am not sure if this is an intentional omission because there is no such constraint or if implementers are not supposed to overwrite. All the current implementers do not overwrite, they append.

[lrhn]

The class has no class documentation at all. It probably should have some.

The documentation for write is

/// Writes the string representation of object.

There is no definition of what "write" means at all. The StringSink is an abstract interface,
so it doesn't enforce any specific implementation. It's intended that the underlying class defines what writing
a string means.
(The sink could be writing directly to an output pipe, so "overwriting" doesn't necessarily mean anything.)

Sequentially writing strings should mean something, so just ignoring a prior write is probably not useful.
But that depends on what the target is. It should at least not be something the client needs to worry about,
if they want to write a sequence of characters, then a StringSink allows that, and where that sequence goes
or how it's interpreted depends on who the receiver is.