SheetJS File Format Notes

Number Formatting

ECMA-376 includes general guidelines for number formatting specifiers. MS-XLS has a sketch ABNF grammar

Auto-Correcting Number Formats

Google Sheets and other third party writers employ number formats that are do not follow the formal grammar. Excel will transparently auto-correct them when round-tripping. Some of the known autocorrections are listed below:

Format Correction
d.m d\.m