DEPR: lower/uppercase strings such as 'y', 'q', 'H', 'MIN', etc. denoting freqs/units for time series, period, and timedelta
xref #52064, #54061

Deprecated lowercase strings in favour of uppercase strings denoting:

- period aliases weekly, monthly and bigger frequency
- offsets aliases representing `DateOffset` subclasses that are a week or bigger (``Week``, ``MonthBegin``, ``MonthEnd``, etc.)
- timedelta units for week, month or bigger

Deprecated uppercase strings in favour of lowercase strings denoting:

- period aliases hourly, minutely or smaller frequency
- offsets aliases representing `DateOffset` subclasses that are an hour or smaller (``Hour``, ``Minute``, etc.)
- timedelta units for hour, minute or smaller
This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. shall we mark this as draft until we've enforced the deprecations already in? > shall we mark this as draft until we've enforced the deprecations already in?

thank you, good idea. I marked this PR as draft. partially closed via #59051 and #58998.
It's still allowed to use mixed cases such as: "Min", "Us", "uS", "Ns", etc.