Where can I find the grammar guide for Excel format syntax? [closed]

Try this Microsoft article "Review guidelines for customizing a number format"

A number format can have up to four sections of code, separated by semicolons. These code sections define the format for positive numbers, negative numbers, zero values, and text, in that order.

   <POSITIVE>;<NEGATIVE>;<ZERO>;<TEXT>

For example, you can use these code sections to create the following custom format:

   [Blue]#,##0.00_);[Red](#,##0.00);0.00;"sales "@

You can use these Custom formats to put Negative Numbers in Red color, inside Brackets with Minus Sign, and Positive Numbers without Brackets and any Sign in Black Color, (which can be Blue or Even Green also).

[Black]#,##0.00_);[Red](-#,##0.00);0.00

#,##0.00_);[Red](-#,##0.00)

For example:

99,000.00

This Custom Format will show Negative Number with Minus Sing in Black Color without Brackets.

#,##0.00_) -99,000.00

For more details you can check these Web Sites:

https://exceljet.net/custom-number-formats

https://www.ablebits.com/office-addins-blog/2016/07/07/custom-excel-number-format/

Note, Color codes [Black] & [Red] are editable and should like, [Blue] or [Green].