The CompTIA Tech+ Study Guide (Exam FC0-U71, 3rd Edition, 2025) defines hexadecimal as follows:
"The hexadecimal notational system, or base-16... In hex, the numbers 0 to 9 are used, just like in decimal.
However, the letters A to F are used to represent decimal numbers 10 through 15." This directly confirms that hexadecimal uses digits 0-9 and letters A-F.
Verified Reference:
* Chapter 6: Software Development Concepts - "Notational Systems" (pp. 357-359).