At any given time text is being output through a selection of "output streams" (possibly none, possibly several at once).

7.1.1

Two output streams are common to all Versions: number 1 (the screen) and 2 (the game transcript, usually printed to a printer or a file).

7.1.1.1

In Versions 1 to 5, the player's input to the read opcode should be echoed to output streams 1 and 2 (if stream 2 is active), so that text typed in appears in any transcript. In Version 6 input should be sent only to stream 1 and it is the game's responsibility to write to the transcript.

7.1.1.2

In Infocom's Version 4 game 'A Mind Forever Voyaging', which anticipated a printer rather than a file to receive the transcript, stream 2 is turned off and on again several times in quick succession. Thus if an interpreter decides where to send the transcript by asking the player for a filename, this question should only be asked once per game session, not every time stream 2 is selected.

7.1.2

Versions 3 and later supply these and two other output streams, numbered 3 (Z-machine memory) and 4 (a script file of the player's whole commands and of individual keypresses as read by read_char).

7.1.2.1

Output stream 3 writes to a table in dynamic memory. When the stream is selected, the table may have any contents (even the initial 'size' word will be ignored by the interpreter). While the stream is selected, the table's contents are unspecified (and a game cannot safely read or write to it). When the stream is deselected, the initial word of the table holds the number of characters printed and subsequent bytes hold those characters. Similarly, in Version 6, the total width of printing (in units) will then be stored in the word at $30 in the header. (It is the programmer's responsibility to make the table large enough: the interpreter performs no overflow checking.)

7.1.2.1.1

*** It is possible for stream 3 to be selected while it is already on. If this happens, the previous table address is remembered and the previous table is resumed when the new one is finished. This nesting can reach a depth of up to 16: if stream 3 is opened for a seventeenth time, the interpreter should halt with an error message.

7.1.2.2

Output stream 3 is unusual in that, while it is selected, no text is sent to any other output streams which are selected. (However, they remain selected.)

7.1.2.2.1

Newlines are written to output stream 3 as ZSCII 13. (A game should never print_char the value 10, or any other value which is undefined as a ZSCII output code.)

7.1.2.3

Output stream 4 is unusual in that, when it is selected, the only text printed to it is that of the player's commands and keypresses (as read by read_char). (Each command is written, in one go, when it has been finished: a command which has been timed-out, or has been terminated by a code in the terminating character codes table, is not written. Mistypes and uses of 'delete' are not written.)

Note that the requirement 7.1.2.1.1, that usages of stream 3 can be 'nested', is new in Standard 1.0. This is potentially important for Inform games, as stream 3 is often used to examine text before printing, for instance to choose between the articles "a" and "an" in front of an object name. But the process of printing an object name may itself require a usage of stream 3, and so on.

An ambiguous point about output stream 4 is whether it should contain the answers to interpreter questions like "what file name should your saved game have?": it can actually be quite useful to be able to include such answers in test script files. (When running a long script, I often save the game at several places during it, in order to save time in re-running passages.)

An interpreter should be able to write time delays (for timed input), accented characters or mouse clicks into stream 4 (i.e., to a script file). One possible style to record this information might be:

    take lamp              an ordinary command
    turn it on.[154]       command, full stop, then keypad 9
                           (which might abbreviate for NE)
    look unde[0]           timed out input
    look under the rock    the same input continuing
    [254][10][6]           mouse-click at (10,6)

A typical auxiliary file might be one containing the player's preferred choices. This would be created when he first changed any of the default settings, and loaded (if present) whenever the game started up.