Which character or characters should be used to represent millisecond and nanosecond in time_key_format.

[Claych]

So far, few customers ask us to support milliseconds and nanoseconds for output plugins kinesis_streams and kinesis_firehose. I have created an extensional function to strftime() to support milliseconds and nanoseconds and decided to use '%3N' to represent millisecond, '%9N' and '%L' can both support nanosecond.
I decided to use %L to represent nanosecond because I found some use cases in Fluent-bit like here. And this document inspires me to use %3N and %9N to represent millisecond and nanosecond in time_format. Also, this document from Fluentd shows the same use with %3N, %9N and %L.
Here is the PR.
Related issue.
Also I have additional options with only using %3N and %9N to represent millisecond and nanosecond which will be easier for customers to use. Or only using %3N and %L to represent millisecond and nanosecond which maybe more consistent with Fluent-bit.
Please give me some suggestions about this and we can have further discussion here . Thank you!

[Claych]

Discussed with @edsiper separately and he liked the suggested formatters with %3N and %9N or %L to represent millisecond and nanosecond which mentioned by Fluentd document.