Updated by @lannka on 4/3/2017:

Use cases:

• Adobe Analytics does not like - (dashes) in client ids, which could be enforced with such a mechanism.
• Google Analytics has cookie value in format of GA1.1.12345.54321, and we want to extract the 12345.54321 part to report as Client ID.

V1

• Introduce a regex filter, which would address most requirements.

V2

• Introduce other filters, such as

 Not (negation)
 Trim
 JSON.stringify
 Base64
 Default()
 ToLowerCase
 ToUpperCase

Task break down:

• Finalize the design of filter syntax.
• Implement rule parser
• Implement filter