Attached below is a brief summary of ICU's number parsing behaviour (data collected using ICU4C 49.1.2)

The following data will be parsed successfully regardless of the pattern or strict/lenient parsing mode

• Digits 0-9
• Decimal Separator
• Exponent Separator

Grouping separators are only permitted in the data, if specified in the pattern


When in STRICT mode the following will cause a parse failure (using a pattern of  "#,##0.#")

• Leading or doubled grouping separators
  ',123' and '1,,234" fail
• Groups of incorrect length when grouping is used
  '1,23' and '1234,567' fail, but '1234' passes
• Grouping separators used in numbers followed by exponents
  '1,234E5' fails, but '1234E5' and '1,234E' pass ('E' is not an exponent when not followed by a number)

• 'Other' characters in the pattern must be present in the data. For example, with a pattern of 'z'## :-

        z12 will parse successfully, 12 will only parse successfully in lenient mode.

Regards

Richard
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