\w+a Unicode word character, repeated at least once
\s*a Unicode whitespace character, repeated any number of times
:the literal : (5810 / 728 / 3A16)
.*?any Unicode character (except for line terminators), repeated any number of times
Positive Lookahead(?=(?:\w+\s*:)|$) 1st Alternative(?:\w+\s*:) Non-Capturing Group(?:\w+\s*:) \w+a Unicode word character, repeated at least once
\s*a Unicode whitespace character, repeated any number of times
:the literal : (5810 / 728 / 3A16)
$end of string, or before its final line terminator
g modifier: global. Finds all matches instead of stopping after the first