This plugin is part of a suite of plugins that comprise the Backstage search
platform. This particular plugin is responsible for all aspects of the search
indexing process, including:
Providing connections to search engines where actual document indices live
and queries can be made.
Defining a mechanism for plugins to expose documents that they'd like to be
indexed (called collators).
Defining a mechanism for plugins to add extra metadata to documents that the
source plugin may not be aware of (known as decorators).
A scheduler that, at configurable intervals, compiles documents to be indexed
and passes them to a search engine for indexing.
A builder class to wire up all of the above.
Naturally, types for all of the above.
Documentation on how to develop and improve the search platform is currently
centralized in the search plugin README.md.
For a better overview of how the search platform is put together, check the
Backstage Search Architecture
documentation.