For illustration purposes, in this documentation redirect pages are in italics: Mainpage → Main_Page

Expect 'yes': {{Is redirect|Autism spectrum}} → yes

Expect '<blank>' (no): {{Is redirect|Autism}} →

By default, a check specifying a talk page is performed on the corresponding subject page (it's associated page in mainspace, or in Template space, etc.).

To check the talkpage itself, both use |talk=yes and the talk page name.

{{Is redirect|Talk:Autism spectrum|talk=yes}} →

Background. By default, when entering a Talkpage to check (like Talk:Autism spectrum), the check is performed on the subject page. This stems from the module used. For example:

Page to check: Talk:Autism spectrum: {{Is redirect|Talk:Autism spectrum}}

Current pages status: Autism spectrum is a redirect, Talk:Autism spectrum is not a redirect (it has content).

{{Is redirect}} returns:

{{Is redirect|Autism spectrum}} → yes Y

{{Is redirect|Talk:Autism spectrum}} → yes ? (unexpected for the talkpage itself)

Applying Talk:Autism:

{{Is redirect|Talk:Autism spectrum|talk=yes}} → Y

Applying the subject page Autism:

{{Is redirect|Autism spectrum|talk=yes}} → yes Y (|talk=yes for a subject page name checks the subject page, not the associated talk page)

• Main Page (expect neg): {{is redirect|Main_Page}} →
• Mainpage (expect yes): {{is redirect|Mainpage}} → yes

Can be used as:

{{#if:{{Is redirect|somepagename}} |value when yes |value when no}}

• {{no redirect}}, {{-r}} — link to the redirect page itself, not its target
• {{target of}} — returns the target of a redirect
• {{redirect}} — hatnote "Foo redirects here ..."
• {{Redirect and target}}