Using “should be” meaning like “will be”?

Question

CloudEdit is an extremely simple document editing app. Here are the specs:

Users should see a list of the latest documents. To edit, the user clicks the document in the list. Users should be able to edit documents with a title and body, and should be able to save their edits to the server. Users should be able to create new documents.

In the paragraph above, we can see that the auther using should be, but It's kind of means "will be", means something like "if you open it, you will see...blah". What is the grammar behind this?

Answer 1

It's common to use this language in a specification to indicate the desired behavior of features that may or may not yet have been written.

Specifications I have read (usually in the form of PRDs -- product requirements documents) tend to use the more assertive "will".

However, it's not ungrammatical to use "should." The Chicago Manual of Style says:

Should often carries a sense of expectation.

Answer 2

Firstly, it's important to realize that will be wouldn't be a correct usage. It's either "users are able to..." or "users can..." or, as the author wrote, "users should be able to...".

It's an unusual way of stating the program features, but I can find two very good reasons why the author could have decided to say it like that:

1) The program is open-source. Whether its features work or not depends heavily on how the users test it, report bugs and how often the community upgrades the code. Therefore they are humbly saying that, "this feature is implemented and it should work. We hope it will." Unlike applications or games coded by huge companies for huge amounts of money tested by huge amount of testers where the final product "simply works."

2) The usage may be derived from a change log. They could have added the features on-the-go, presenting them as "we have implemented function X. Now users should be able to open a list of..." If a change log becomes full of such statements, they may be later copied to the features section.

TL;DR: The style is grammatical. It's a humble way of presenting own work. There are alternatives, but it depends on the context what is best to use when.