(?si)applies the following effective flags to the remainder of the pattern: gmsi s modifier: single line. Allows a dot to match line terminators
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
FIRST:the literal text FIRST: (case insensitive) .*?any character, repeated any number of times
\s*any whitespace character, repeated any number of times
LAST:the literal text LAST: (case insensitive) .*?any character, repeated any number of times
\s*any whitespace character, repeated any number of times
DOORthe literal text DOOR (case insensitive) .*?any character, repeated any number of times
ID:the literal text ID: (case insensitive) \d+a digit, repeated at least once
g modifier: global. Finds all matches instead of stopping after the first
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string