ne's manual

4.4.11: Through

the standard input, and replacing it with the output of the command. This command is most useful with filters, such as sort. Its practical effect is to pass the block through the specified filter.

Note that by selecting an empty block (or equivalently by having the mark unset) you can use Through in order to insert the output of any UN*X command in your file.

If the optional argument command is not specified, you can enter it on the input line.