string - In PHP, what does "<<<" represent? -

for example:

$sql = <<<mysql_query 

that's heredoc syntax. start heredoc string putting <<< plus token of choice, , terminate putting token (and nothing else!) on new line. convenience, there 1 exception: allowed add single semicolon after end delimiter.

example:

echo <<<heredoc heredoc string.  newlines , else preserved. heredoc;