Why the difference in usage between 'clear' and 'unset' with Rebol lists? -

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given list:

a: [1 2 3 4 5]

why clear a clear list , unset 'a unset it? have expected both clear , unset consistently take either a or 'a arguments.

clear removes entries block referenced word a:

a: [1 2 3 4 5] length? == 5 clear length? == 0

unset removes word a itself:

a: [1 2 3 4 5] length? == 5 unset 'a length? ** script error: has no value ** near: length?

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