# What a page knows about another page

> Every field a listing can use, what each is for, and why a list can show you a page's summary but never a paragraph out of its middle.
>
> From the MightyBuilder documentation: https://docs.mightybuilder.ai/dynamic/what-a-page-knows

A list can only use what a page or an article publishes about itself. That set
is fixed, and it is short on purpose.

## The fields

Inside a loop, each item — and the document you are on, as `page` — has these:

| Field | What it is | |
| --- | --- | --- |
| `title` | The title. | both |
| `url` | Its address, starting with a slash. `/` for the homepage. | both |
| `path` | The same without the leading slash. `""` for the homepage. | both |
| `postId` | Its own identifier. | both |
| `date` | Its publication date. | both |
| `lastmod` | When it last changed. | both |
| `excerpt` | The short summary from its settings. | both |
| `image` | Its own picture, or nothing. | both |
| `tags` | The words it is grouped by, as a list. Empty when it has none. | both |
| `parent` | The address of the page, or item, it sits inside, without slashes. `""` at the top level. | both |
| `parentId` | The identifier of that parent, when you need the id rather than the address. | both |
| `order` | Where it sits among its siblings, as a number. | both |
| `fields` | Its values for its collection's fields — `p.fields.client`. See [Collections](/dynamic/collections). | items |

`parent`, `parentId` and `order` place a document among its siblings. A page
sits in the page tree. An item sits in its own collection, in the order you
dragged it into, and has a parent only when its collection is hierarchical: in
a flat collection like Articles, `parent` is always `""`. An item never sits
under a page. See [Articles](/dynamic/articles). `fields` is the other way
round: only an item of a collection has one.

`tags` is the one that is a **list** rather than a single value, so it behaves
differently from everything else in the table. `.size`, `.first` and `.last`
work on it — as they do on `site.pages` and `collections.articles` — and nothing else
does: to read the words, loop over it or use `| join`. See
[Tags](/dynamic/tags).

## One shape, current document or listed one

`page.title` and `post.title` inside a loop mean the same thing, because they
are the same shape. A block written against one works against the other, which
is what lets a card design be used by an index and by the page itself.

`page` means **whatever is being served** — a page or an article. There is also
`item`, which is set only while an article (or any collection's item) is being
served, for the times a shared block needs to tell:

```liquid
{% if item %}
  <p class="byline">Published {{ page.date | date: "%-d %B %Y" }}</p>
{% endif %}
```

A block that reads `{{ page.parent }}` on an article gets an empty value rather
than an error, because an article in a flat collection has no parent. That is
what lets one header work on both without being written twice.

The one place this is deliberately strict: **`image` is the page's own picture
and never falls back to the site's.** A field that meant something different on
the current page than on a listed one would break exactly that property.

## A picture has its own fields

When a page has one:

```liquid
{% if page.image %}
  <img src="{{ page.image.src }}" alt="{{ page.image.alt }}">
{% endif %}
```

`src` and `alt` are always there. `width`, `height`, `avif` and `webp` are
present for an uploaded photograph and absent for an external image or a vector,
so guard those the same way if you use them.

## What a list cannot reach

**The body of another page or article.** A loop can show you a title, a summary
and a picture — it cannot show a paragraph out of the middle of something.

That is a deliberate line rather than a gap. The index is built from a compact
record of every page and article; reaching into bodies would mean loading the
whole site to render one listing.

If you want a sentence from an article to appear on the index, put it in that
article's **excerpt**. That is what the field is for.

## Getting a field name wrong

You cannot, quietly. A name that is not on the list above stops the site
publishing, and the message names the field and lists the real ones. See
[When something is wrong](/dynamic/when-something-is-wrong).