Does anyone know set of valid characters in DataWindow column's DBName property for external DataWindows?

I can't find info in F1-Help so trial-and-error gave me below list of valid characters. It may be incomplete.

• Uppercase letters A - Z
• Lowercase letters a - z
• Digits 0 - 9
• Underscore, dollar-sign
• Non-English letters -- I verified: Æ æ Ø ø Å å á é í ä ë ñ

To my surprise, dot and space are invalid characters despite appearing when source is a database.

Thanks for any pointers /Michael

PS: Why I want to know?
I have external DW for SaveAs(XLSX) to govern column header texts, reorder columns, save display values, and skip irrelevant columns.

Total export contains 20'000+ data items.