The tail operator:

• can only be applied to string values and byte vectors
• can only replace the end of e.g. a string value
• cannot shrink the size of a string value, only grow or remain in size
• cannot create output field value if delta value is not present in the stream

The delta operator:

• can be applied to numbers, strings and byte vectors
• can replace either the beginning or end of a string value
• can shrink the size of a string
• can use just previous or initial value (if tail value is not present in the stream) for the output field value.