\ban ASCII word boundary
UAthe literal text UA (case sensitive) \s?optionally matches any whitespace character
\d{2}a digit, repeated exactly 2 times
\s?optionally matches any whitespace character
\d{6}a digit, repeated exactly 6 times
\s?optionally matches any whitespace character
\d{19}a digit, repeated exactly 19 times
\ban ASCII word boundary
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