Source

File: wp-includes/pomo/entry.php

function key() {
			if ( null === $this->singular || '' === $this->singular ) {
				return false;
			}

			// Prepend context and EOT, like in MO files.
			$key = ! $this->context ? $this->singular : $this->context . "\4" . $this->singular;
			// Standardize on \n line endings.
			$key = str_replace( array( "\r\n", "\r" ), "\n", $key );

			return $key;
		}