Cldr.DateTime.Format.common_date_time_format_names

You're seeing just the function common_date_time_format_names, go back to Cldr.DateTime.Format module for more information.
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common_date_time_format_names(backend \\ Cldr.Date.default_backend())

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Returns a list of the date_time format types that are available in all locales.

The format types returned by common_date_time_format_names are guaranteed to be available in all known locales,

Example:

iex> Cldr.DateTime.Format.common_date_time_format_names
[:bh, :bhm, :bhms, :d, :e, :e_bhm, :e_bhms, :e_hm, :e_hms, :ed, :ehm,
:ehms, :gy, :gy_mm_md, :gy_mmm, :gy_mmm_ed, :h, :hm, :hms, :hmsv,
:hmv, :m, :m_ed, :md, :mm_md, :mmm, :mmm_ed, :mmm_md,
:mmmmw_count_other, :ms, :y, :y_m, :y_m_ed, :y_md, :y_mm_md, :y_mmm,
:y_mmm_ed, :y_mmmm, :y_qqq, :y_qqqq, :yw_count_other]