MyApp.Cldr.Number.Symbol.all_decimal_symbols_class

You're seeing just the function all_decimal_symbols_class, go back to MyApp.Cldr.Number.Symbol module for more information.
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all_decimal_symbols_class()

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Returns a list of all decimal symbols defined by the locales configured in this backend as a string.

This string can be used as a character class when builing a regular expression.