Add new site under multisite helper text

[Clorith]

When adding a new site to a multisite setup, you can define the address and the helper text states Only lowercase letters (a-z) and numbers are allowed., but you can still use dashes (no underscores though)

Rather trivial, but if people don't know they can use them one might get domain.com/myawesomesitenobodycanread as opposed to domain.com/my-awesome-site-people-can-read.

I'm not familiar with the decision around what is blocked for the address, but one view could be that not blocking dashes is an oversight as well, since underscores are blocked?

[jeremyfelt]

Related: #17397, #20019, #17904

[thomaswm]

26388.diff​ changes the text which is displayed on the "Add new site" page.

[jeremyfelt]

In 35893:

MS: Update "Add New Site" address description text for accuracy.

Add hyphens to the list of allowed characters and add the description class to helper text paragraph tag.

Props thomaswm for the initial patch.
Fixes #26388.

[SergeyBiryukov]

Add hyphens to the list of allowed characters

Should the regex and the message in wpmu_validate_blog_signup()​ also be updated?

[jeremyfelt]

Replying to SergeyBiryukov:

Should the regex and the message in wpmu_validate_blog_signup()​ also be updated?

Clearing up the inconsistencies between the add/edit/signup flows for sites should probably be covered in #20019 and #17397.