What are the consequences of this? Why is this important to note here? What is the meaning of the extension element with the cardinality 0..0?

These are the immediate questions I am getting from this statement.

Please consider addressing them here or removing this sentence, in case it is not important for this walk-through

Existing Wording:

Since extensions in FHIR only allow value[x] or extension elements, the extension element will automatically have its cardinality set to 0..0.