Salesforce REGEX - Detect Chars not working as expected

I have the following situation in Salesforce: A certain fields contains one string. But this string char's all have a significant meaning.

For instance, the string can look like: GHJKL where G, H, J, ... have a certain meaning which is being used in code.

What I would like to do now is perform a Validation on the entered String with following conditions:

Only the chars: GHJKL can be entered
The char G AND/OR H must be entered at east once

I have following REGEX which detects that only the above chars can be entered:

For the first Validation:

'NOT(REGEX(CustomFieldName__c,"[ABCDEI]{0,30}"))'
For the Second Validation:

'NOT(REGEX(CustomFieldName__c,"[DE]{1,}"))'

But the second validation seems not be working. I've tested the Regex using online Regex tester where this seems to be working. But on Salesforce, the regex is constantly providing a False.

Any ideas?

Thanks!

Solution

This should be regex for second validation for You

(?=.*D)(?=.*E).*|[DE]+

Thanks to Regex AND operator