Tardis:Subpage policy

What is a subpage?
Doctor Who Magazine/1985 is an example: because of the slash in the page name, it's a subpage of Doctor Who Magazine, so there's a link to that page right at the top, just below the title. This is great for navigation! Fandom's Editor Experience team explains,

Additionally, a subpage can also be linked to from its parent page with only a partial title: if you're on Twelfth Doctor, the link  will take you to Twelfth Doctor/Appearances. It's even more powerful than the pipe trick!

If subpages are so useful, why aren't they used on wikis more widely? In 2001, a lengthy debate on Wikipedia resulted in a new rule: This was to avoid fights like whether to create History/Algeria or Algeria/History. Because subpages had provided a home for material about fictional universes – for instance, Doctor Who/Sonic screwdriver – this presaged a slow exodus of that content away from Wikipedia.

Tardis Data Core was born from that exodus, and ever since we've said we're Wikipedia's evil twin. This means we're free to reconsider Wikipedia's decisions with fresh eyes, including the rule about subpages. The conclusion is that our finite set of standardised section names means we can avoid the confusion that caused Wikipedia's ban in the first place!

How big is too big?
According to the Editor Experience team,

When to use a subpage
Subpages are usually only meant to be linked to from their root page and navigation templates. To use the example mentioned above, Twelfth Doctor - list of appearances was only linked to from Twelfth Doctor and, making it an obvious candidate for a subpage.

Subpages should be named after section headers, usually those with headings formatted with ==, such as "Biography" or "Plot". Subpages should never have in-universe titles: for instance, if the subsection Twelfth Doctor were deemed too big, we would move it to a section on Twelfth Doctor/Biography, not Twelfth Doctor/Continued adventures with Clara.

Subpages are also used to sequester spoilery information on a real-world topic which also calls for documentation of non-spoilery information.

Here's a sample of other potential subpage names:
 * BBC New Series Adventures/Covers
 * Twelfth Doctor/Appearances
 * David Tennant/Spoilers

To prevent the unsustainable proliferation of subpage types that Wikipedia faced, a wholly new type of subpage should be discussed on the talk page beforehand. For instance, if you want to create Series 9 (Doctor Who)/Promotion for information about trailers and interviews promoting that series, first you should compare your idea against existing precedent. If /Promotion subpages already exist in other places, you can go ahead and create your page! Otherwise, you should propose it on Tardis:Temporary forums, and allow an administrator to conclude the discussion before your split.

When not to use a subpage
Alternately, if you think some material represents a self-contained idea that other articles might want to reference as well, consider splitting it without using a subpage. For instance, when conflicting accounts of the Doctor's origins on First Doctor became too unwieldy, The Doctor's early life was created. Other examples include pages for specific arcs, like Exile on Earth, or pages for specific events, like Operation Mannequin. This is an art, not a science, and experienced users should use their best judgment to decide how to group content into logical topics.

Here are some examples of when not to use a subpage:
 * Third Doctor/Exile on Earth – instead create Exile on Earth
 * The Doctor/Sonic screwdriver – instead create The Doctor's sonic screwdriver
 * Aliases of the Doctor/Theta Sigma – instead create Theta Sigma
 * Last Great Time War/Origins – instead create Origins of the Last Great Time War
 * The Master/Missy – instead create Missy!

Moving material
Once you've identified a lengthy section and the new page or subpage that will hold it, cut the section's contents and paste it to the new location. Include any subheadings, images, galleries, footnotes, and infoboxes that are inside that section. Subheadings should be adjusted upwards: for instance, each === subheading should become a ==.

Look through Special:WhatLinksHere to update any redirects to the sections you've moved. Similarly, look through the original page's templates and "Behind the scenes" bullet points for any which are more relevant to the new page. One of the biggest advantages of subpages is that they provide more room for not just ordinary coverage but also specific templates and sections.

Most importantly, Tardis:Plagiarism requires that you credit the content's original authors per CC BY-SA 3.0. When you're moving material to a subpage, it's usually obvious where it came from, but you should still link to the original page in your edit summary so later readers know where to look for the edit history.