+=item -f, --field=(<number>|<regexp>)
+
+Compare values after a given number of whitespace separators,
+or matching a regular expression.
+
+Unspecified or I<-f0> means values are at the start of each line.
+With I<-f1> the second word is taken instead.
+A string can indicate the starting position of a value
+(such as I<-f:> if preceded by colons),
+or capture the numbers itself,
+for example I<-f'(\d+)'> for the first digits anywhere.
+