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This website is very learnable because everything you need to remember is on your main page. All you have to do is remember to go there and read the options there. Long term memory is not required.
Efficiency:Safety:
There are two steps to finding a project. Logging in and searching. Similarly, to do any of the features you only need to through the main page so there are no long chains. That being said it may be inefficient to always have to go through the main page and it may have been better if all pages were linked to each other, but that may cause a learnability issue. Perhaps it could be useful feature for advanced users.
Safety:
If nothing on this website were permanent then it would be good for deleting errors and bad for saving good things accidentally destroyed. If you delete a project and you were the host, you can not be the host again unless you open a new project (or if we implement auto host switching and manual host transfers - if you ask the newly appointed host to give you back hostship). There are no steps to sewing (so they aren't irreversible) and you can get as much help as your sewing mates will give you. If you lose a search you will have to re-search. If you delete a note it stays deleted.
So to make this site safe we shoudl back up all the user's data and give them intrusive confirmation boxes for when they want to do something permanently destructive (concerns are deleting a project, deleting notes, deleting images)