DB<135> $str = "\tstart\tmiddle1\t\"quote1\tquote2\"\tmiddle2\tend\t"; 
 => "\tstart\tmiddle1\t\"quote1\tquote2\"\tmiddle2\tend\t"

  DB<136> $str .= "\n$str"
 => "\tstart\tmiddle1\t\"quote1\tquote2\"\tmiddle2\tend\t\n\tstart\tmiddle1\t\"quote1\tquote2\"\tmiddle2\tend\t"

  DB<137> p $str
	start	middle1	"quote1	quote2"	middle2	end	
	start	middle1	"quote1	quote2"	middle2	end	
 => 1

  DB<138> p $str =~ s/ (?<=[^"]) \t (?!"|$) /***/gmxr
	start***middle1	"quote1***quote2"	middle2***end	
***start***middle1	"quote1***quote2"	middle2***end	
 => 1

  DB<139> p $str =~ s/ (?<!")(?<!^) \t (?!"|$) /***/gmxr
	start***middle1	"quote1***quote2"	middle2***end	
	start***middle1	"quote1***quote2"	middle2***end	
 => 1