Re^2: " - " in the syntax

This got me curious

$ perl -MO=Deparse -e 'print $q -> start_html(-title => "The Time", -b
+gcolor => "#ffffff") '
print $q->start_html(-'title', 'The Time', -'bgcolor', '#ffffff');
-e syntax OK

$ perl -MO=Deparse -e 'print -"asdf"'
print '-asdf';
-e syntax OK

$ perl -MO=Deparse -e 'print -"1asdf"'
print -1;
-e syntax OK

$ perl -MO=Deparse -e 'print -"-1asdf"'
print '+1asdf';

$ perl -MO=Deparse -e 'print -"+1asdf"'
print '-1asdf';
-e syntax OK
[download]

What I glean from this is that if you use unary minus on any non-numish-looking string constant, the minus will get prepended. If you use an undecorated(+/-) numish string constant it gets numified, but if you use a decorated one it inverts the sign and doesn't numify?

Is this accurate?
Is this documented anywhere?
What is the rule on this?
And what is this useful for (beyond use given in the OP)

Comment on Re^2: " - " in the syntax Download Code

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Re^3: " - " in the syntax by puudeli (Pilgrim) on Mar 06, 2009 at 06:04 UTC
Did you read Symbolic-Unary-Operators? `$ perl -MO=Deparse -e 'print -"asdf"' print '-asdf'; -e syntax OK` [download] If the operand is an identifier, a string consisting of a minus sign concatenated with the identifier is returned. `$ perl -MO=Deparse -e 'print -"1asdf"' print -1; -e syntax OK` [download] If, however, the string begins with a non-alphabetic character (excluding "+" or "-"), Perl will attempt to convert the string to a numeric and the arithmetic negation is performed. `$ perl -MO=Deparse -e 'print -"-1asdf"' print '+1asdf'; $ perl -MO=Deparse -e 'print -"+1asdf"' print '-1asdf'; -e syntax OK` [download] Otherwise, if the string starts with a plus or minus, a string starting with the opposite sign is returned. -- `seek $her, $from, $everywhere if exists $true{love};`	[reply] [d/l] [select]
Re^4: " - " in the syntax by Anonymous Monk on Mar 06, 2009 at 09:27 UTC
Symbolic_Unary_Operators	[reply]
Re^4: " - " in the syntax by Anonymous Monk on Mar 06, 2009 at 09:27 UTC
Symbolic_Unary_Operators	[reply]


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