[tz] Use cases for source data

[Stephen Colebourne]

On Fri, 8 Oct 2021 at 02:33, Gilmore Davidson via tz <tz at iana.org> wrote:
> 1) The zic compiler for producing TZif binary files and .zi text files in an official tzdb release.
>
> 2) People reading the file comments to understand the history of certain zones.
>
> 3) Libraries/projects that need to parse/compile the data into a different representation than that provided by zic. This is often, but not exclusively, to preserve the distinction between Link and Zone entries, either for API or data compression reasons.
>
> 4) Data analysis or visualisations that care about knowing the higher-level Rule definitions ("transition on the last Sunday of October every year") rather than the exact transition timestamps for each year.
>
> 5) IDE or text editor plugins that provide syntax highlighting for the source files.

The Java projects I've initiated use the source files to extract the
history of previous transitions, and the Rule that expresses what will
happen in the future. Information about the rule is fully exposed in
the API of java.time.*
https://docs.oracle.com/javase/8/docs/api/java/time/zone/ZoneRules.html
https://docs.oracle.com/javase/8/docs/api/java/time/zone/ZoneOffsetTransitionRule.html

Stephen