Not sure that ValidatePattern could be specified twice for one parameter or that you could have it check against multiple patterns. It would probably be better to have a single pattern match. What are the possible computer names? Do you have any regex patterns built?
Regex has an "or" operator (the pipe symbol) that can be used to combine two patterns into a single regex. However, the ValidatePattern attribute produces error messages that are extremely unfriendly to users, and its use is generally discouraged. Using ValidateScript, you can get the same functionality, but also produce any error messages you like via the "throw" statement.
Thank you everyone for your assistance. Please excuse my late response.
I used the "|" pipe sign to combine two Regex-s because I needed it for my function which creates Gen2 VMs on my Hyper-V server and I wanted them to be according to my naming standards: for virtual servers i.e. "VM-Server-DC01" and for virtual workstations i.e. "W81Ent01".