\Astart of string
*?matches any number of characters from the set below:
\sany whitespace character
\Sany non-whitespace character
\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
"FECHAthe literal text "FECHA (case sensitive) \sany whitespace character
DEthe literal text DE (case sensitive) \sany whitespace character
EMISIONthe literal text EMISION (case sensitive) .*any character (except for line terminators), repeated any number of times
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