Providing a command guide is helpful for all computer games, not just parser or IF.
If a player has anxiety, being able to see the commands before starting gives confidence that the game is completable - even if that player proceeds never to look at it again, or even note any of the specific commands.
People with memory issues like to be able to refer back to the instructions if they forget. Note that “issues” does not simply encompass people with formal memory disabilities such as dementia, but also people who need to juggle many things in working memory and occasionally drop some (be that due to having difficulties co-ordinating two hands on the keyboard or needing to cook the family dinner at the same time as playing the game because their support aide didn’t turn up for work).
Any disability involving difficulties with context changes would benefit from a command list, to avoid muscle memory trying to use a response that makes sense in a different context but not for this specific game. The source can be as proximate as a similar parser IF or as far away as the security code for a completely different building, since all it takes is for one thing in common, and lots of IF uses keyboards…
Dyslexia increases difficulties with spelling, so a command list means it’s easy to confirm whether one is trying something impossible or is making several varieties of typo.
People who have difficulty taking the perspective of others can use the command list to help them imagine how the IF author (and perhaps the IF’s characters) think about situations. A well-crafted command list can be an aid to character and setting (Zozzled is a good example of this).
And of course, even for experienced players, a command list can help with things that aren’t common in the genre. Deadline’s manual had a command list including the unusual SEARCH NEAR [something], which would be difficult to guess even for someone used to parsers. For my IFComp entry I doubt anyone would guess to SABOTAGE MACHINERY, HIDE BEHIND PANEL, or ANALYZE WEAPON without some sort of prompting.
I don’t know how good Inform 7 is at having multiple panes. I haven’t looked into it. I think some players would appreciate a pane showing verbs. Or other information. I have a “VERBS” command, but I don’t feel that it fulfills the recommendation criteria.
I think it’d be good to let the player see some of this stuff all the time if it helps (it should be optional).
It’s possible in I7 but requires extensions that haven’t yet been updated for the new version. It also requires a bit of cleverness about how you use the space, since it’s hard for the player to reposition them.
I think one often forgotten way to accessibility would be accessible language. By that I mean using as simple vocabulary as possible, avoiding unnecessary complexity in descriptions and keeping the story easy to follow while also engaging readers. Of course that’s easier said than done. Accessible language is different for everyone, and sometimes being artistic might require writing in a less easily understood way.
I’m toying with the idea of including easy to browse definitions and synonym lists in parser based games. I think it would lessen the need for disruptive googling and also help with finding options for difficult-to-type words while preserving some of the challenge for those who want it. This feature would probably require hyperlinking, though.
My wife loves when she can tap on a word on her Kobo and get the definition. The least obtrusive method is best. A tool tip / pop-up definition pulled from a locally stored file. Once a story is finished, you could parse the text and create an array of needed definitions. Then copy the definitions from a full database into your story specific, smaller definitions array.
For example, Princeton has WordNet and has links to download the database files, which can be accessed online too.
Maybe someone has already created the tools to do this.