https://unicode-org.github.io/icu/userguide/format_parse/messages/

{gender_of_host, select,
  female {
    {num_guests, plural, offset:1
      =0 {{host} does not give a party.}
      =1 {{host} invites {guest} to her party.}
      =2 {{host} invites {guest} and one other person to her party.}
      other {{host} invites {guest} and # other people to her party.}}}
  male {
    {num_guests, plural, offset:1
      =0 {{host} does not give a party.}
      =1 {{host} invites {guest} to his party.}
      =2 {{host} invites {guest} and one other person to his party.}
      other {{host} invites {guest} and # other people to his party.}}}
  other {
    {num_guests, plural, offset:1
      =0 {{host} does not give a party.}
      =1 {{host} invites {guest} to their party.}
      =2 {{host} invites {guest} and one other person to their party.}
      other {{host} invites {guest} and # other people to their party.}}}}

{num_guests, selectordinal, foo}

----------------------------------------------------

[
	"https://unicode-org.github.io/icu/userguide/format_parse/messages/\r\n\r\n",

	["argument", [
		["argument-delimiter", "{"],
		["content", [
			["argument-name", "gender_of_host"],
			["punctuation", ","],
			["keyword", "select"],
			["punctuation", ","],

			["select-style", [
				["selector", ["female"]],
				["nested-message", [
					["message-delimiter", "{"],
					["message", [
						["argument", [
							["argument-delimiter", "{"],
							["content", [
								["argument-name", "num_guests"],
								["punctuation", ","],
								["keyword", "plural"],
								["punctuation", ","],
								["plural-style", [
									["offset", "offset:1"],

									["selector", ["=0"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" does not give a party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", ["=1"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" to her party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", ["=2"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" and one other person to her party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", [
										["keyword", "other"]
									]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" and # other people to her party."
										]],
										["message-delimiter", "}"]
									]]
								]]
							]],
							["argument-delimiter", "}"]
						]]
					]],
					["message-delimiter", "}"]
				]],

				["selector", ["male"]],
				["nested-message", [
					["message-delimiter", "{"],
					["message", [
						["argument", [
							["argument-delimiter", "{"],
							["content", [
								["argument-name", "num_guests"],
								["punctuation", ","],
								["keyword", "plural"],
								["punctuation", ","],
								["plural-style", [
									["offset", "offset:1"],

									["selector", ["=0"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" does not give a party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", ["=1"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" to his party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", ["=2"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" and one other person to his party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", [
										["keyword", "other"]
									]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" and # other people to his party."
										]],
										["message-delimiter", "}"]
									]]
								]]
							]],
							["argument-delimiter", "}"]
						]]
					]],
					["message-delimiter", "}"]
				]],

				["selector", [
					["keyword", "other"]
				]],
				["nested-message", [
					["message-delimiter", "{"],
					["message", [
						["argument", [
							["argument-delimiter", "{"],
							["content", [
								["argument-name", "num_guests"],
								["punctuation", ","],
								["keyword", "plural"],
								["punctuation", ","],
								["plural-style", [
									["offset", "offset:1"],

									["selector", ["=0"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" does not give a party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", ["=1"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" to their party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", ["=2"]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" and one other person to their party."
										]],
										["message-delimiter", "}"]
									]],

									["selector", [
										["keyword", "other"]
									]],
									["nested-message", [
										["message-delimiter", "{"],
										["message", [
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "host"]
												]],
												["argument-delimiter", "}"]
											]],
											" invites ",
											["argument", [
												["argument-delimiter", "{"],
												["content", [
													["argument-name", "guest"]
												]],
												["argument-delimiter", "}"]
											]],
											" and # other people to their party."
										]],
										["message-delimiter", "}"]
									]]
								]]
							]],
							["argument-delimiter", "}"]
						]]
					]],
					["message-delimiter", "}"]
				]]
			]]
		]],
		["argument-delimiter", "}"]
	]],

	["argument", [
		["argument-delimiter", "{"],
		["content", [
			["argument-name", "num_guests"],
			["punctuation", ","],
			["keyword", "selectordinal"],
			["punctuation", ","],
			["plural-style", [
				["selector", ["foo"]]
			]]
		]],
		["argument-delimiter", "}"]
	]]
]
