Purpose

Multisite signup handler for new users and/or new sites, including validation and form rendering.

Flow

• Loads WordPress (wp-load.php) and front-end context (wp-blog-header.php).
• Ensures multisite and main-site context; otherwise redirects.
• Registers signup_header and default stylesheet output via wp_head.
• Outputs signup forms and handles submission:
  • Validates user/site data via wpmu_validate_user_signup() and wpmu_validate_blog_signup().
  • Creates signup records via wpmu_signup_user() / wpmu_signup_blog().
  • Optionally creates site immediately for logged-in users (wpmu_create_blog()).

Key functions called

• wpmu_validate_user_signup()
• wpmu_validate_blog_signup()
• wpmu_signup_user()
• wpmu_signup_blog()
• wpmu_create_blog()
• signup_get_available_languages()

Hooks fired

• Actions:
  • signup_header
  • before_signup_header
  • before_signup_form
  • signup_blogform
  • signup_extra_fields
  • signup_hidden_fields
  • signup_finished
  • preprocess_signup_form
  • after_signup_form
• Filters (selected):
  • add_signup_meta
  • wpmu_active_signup