Query regarding format of Azure Subscription id

I wanted to check what all characters can be pres开发者_StackOverflow社区ent in Subscription id of Azure Subscription. I saw documentation here but it mentions format of id as something like 0000-0000-0000-000000000000. It does no tells me what all characters are valid in the format. e.g. can Subscription id contain "_" or any other character

I tried referring documentation but could not find the required information

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Azure subscription ID is a globally unique identifier (GUID). The following article discuss how to validate GUID using Regular Expression. I think it would help you link here