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# Author: Joe Touch / touch@strayalpha.com
# Last update: 7/15/2019

# adds XML <bcp14> tags around capitalized RFC2119 keywords and
# keyword phrases:
#	MUST
#	MUST NOT
#	REQUIRED
#	SHALL
#	SHALL NOT
#	SHOULD
#	SHOULD NOT
#	RECOMMENDED
#	MAY
#	OPTIONAL

# this version requires perl5 v5.30.0 or later with support for vlb

# set things up to use variable look behind, an experimental feature
# as of Perl v5.30.0

use warnings;
use experimental 'vlb';

# pull in the entire file as a single line, suitable for multiline
# search/replace
my $line = do {local $/; <> };

# do the search and replace, but not if the item is preceded by an
# existing <bcp14> tag
#
# note that we can tolerate only 248 whitespace characters inbetween,
# and we're not testing for other tags or characters

$line =~ s/(?i:(?<!<bcp14>\s{0,248}))(\b(((MUST|SHOULD|SHALL)(\s+NOT)?)|((NOT\s+)?RECOMMENDED)|MAY|OPTIONAL|REQUIRED)\b)/<bcp14>$1<\/bcp14>/g;

# note - due to use of backtracking, no need to get rid of possible
# duplicates

# output the result
print $line;