Special characters in custom date formats

[NormThib]

I see some custom date codes in my spreadsheet include special characters. I have found some excellent documentation on special date and number formatting on the web, but I have not not been able to find any info on these special characters. I'd like to know what they mean and how/when to use them. Can you help? Here are some of the custom date formats I see with special characters:
m/d/yy;@
[$-en-US]dddd, mmmm d, yyyy
_($* #,##0_);_($* (#,##0);_($* "-"_);_(@_)
The above use the following special characters:
;@
[$-en-US]
_($*
_);_

 

[jasonb75]

I have found some excellent documentation on special date and number formatting

It couldn't have been that good if it didn't cover some of the basics that you're asking about.

; separates the four sections of the format (positive numbers, negative numbers, zero values, text)

@ signifies text

[$-en-US] signifies default formatting based on regional settings, so dates will appear as M/D/Y in the US and D/M/Y in the UK.

* pads the cell (by repeating the space after the * as many times as needed) so that the $ symbol is set to the left side, with the amount to the right. Without the * the $ symbol would be next to the amount.

_ is for inserting a space into the format. I believe that this inserts a space that is slightly wider than normal for alignment purposes, but I have never had cause to look at this in detail.

The parenthesis are not in any of the default UK formats (or not that I have found), they appear to be used to preserve other parts of the formatting as necessary. Attempting to remove any of them from the format causes some strange results or rejection of the format as invalid.