Description:
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In the Description section of the documentation, for DateTime::add() the 
variable type for $interval is said to be "string", but for the 
procedural equivalent, date_add() the variable type for $interval is 
said to be "DateInterval".

However, in the Parameters section of the documentation, the type for 
$interval is only said to be "DateTime" and there is no mention of 
"string".

This is inconsistent - though I am not clear whether the Description 
section is correct and the Parameters section is wrong, or vice versa.

Reproduce code:
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From manual page: datetime.add#Description
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Expected result:
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Not applicable.

Actual result:
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Not applicable.