Alternatives 
p1p2…
is a pattern object that represents any of the patterns pi.
Details

- If a named pattern such as x_ appears in pi that are not used in a particular match, then the named pattern is taken to have a value that is a zero-length sequence Sequence[].
Examples
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Wolfram Research (1991), Alternatives, Wolfram Language function, https://reference.wolfram.com/language/ref/Alternatives.html.
Text
Wolfram Research (1991), Alternatives, Wolfram Language function, https://reference.wolfram.com/language/ref/Alternatives.html.
CMS
Wolfram Language. 1991. "Alternatives." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/Alternatives.html.
APA
Wolfram Language. (1991). Alternatives. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Alternatives.html