Keywords - Importance of multi word keyword against single keywords

A keyword list consists the following keywords

word one, two, word three

According to Apple I can repeat keywords in the keyword field. If this is the case does that mean the Apple will not add as much weight to or even combine a word in a 2 word phrase with a 1 word phrase?

Example: I search for word one and Apple finds because it is in my keyword list. What happens if I want to look for word two? Will Apple combine the keywords and locate word two and if so will Apple add as much weight to it? I am guessing it won't because it isn't exact.

I am wondering if it is better to add single keywords i.e word,one,two and let Apple combine them.

Keywords - Importance of multi word keyword against single keywords
 
 
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