ISO 8601

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HTML

1	2	3	4	5
1582-10-15	1582‑10‑15	1582‑10‑15	<nobr>1582-10-15</nobr>	1582-10-15

@1 using - (U+002D hyphen-minus)
@2 using "&#X;" with X=8209 (U+2011 non-breaking hyphen) - search for 1582-10-15 (method 1) possibly does not match
@3 using the sign itself (U+2011 non-breaking hyphen) - search for 1582-10-15 (method 1) possibly does not match
@4 using nobr-tag around method 1
@5 using span style="white-space: nowrap;"

Glibc

http://www.gnu.org/software/libc/manual/html_node/Formatting-Calendar-Time.html

%F = %Y-%m-%d

PHP

http://php.net/manual/en/function.date.php

Y-m-d

Y, m, d as in Glibc
F differs from Glibc and means "A full textual representation of a month"