# Passing something into a block

> What lets one card design serve a blog index, a homepage strip and a section page without becoming three near-identical copies of each other.
>
> From the MightyBuilder documentation: https://docs.mightybuilder.ai/pages/passing-something-in

A block can be handed something to work with, which is what lets one card design
serve a blog index, a homepage strip and a section page without becoming three
near-identical copies.

## The problem it solves

Write a card block that reads the page it is on, and it shows the same thing
everywhere it appears. That is fine for a header and useless for a card in a
list, where each card must show a *different* article.

## Handing something in

On the `render` call, name it:

```liquid
{% assign posts = collections.articles | sort: "date" | reverse %}
{% for post in posts limit: 6 %}
  {% render "aB3x9kQ2mN01", post: post %}
{% endfor %}
```

`post: post` reads as "call it `post` inside the block, and give it the `post`
I am looking at right now". The name on the left is what the block sees.

## Using it inside the block

```liquid
<article>
  <a href="{{ post.url }}">
    {% if post.image %}
      <img src="{{ post.image.src }}" alt="{{ post.image.alt }}">
    {% endif %}
    <h3>{{ post.title }}</h3>
    <p>{{ post.excerpt }}</p>
  </a>
</article>
```

The block now works for any page handed to it, which is the whole point: one
card design, used by every list that wants cards.

## A block only sees what it is given

It does not see what the surrounding page has `assign`ed. If a block needs
something, it has to be passed in — which is what makes a block predictable: reading it
tells you everything it depends on.

## Naming things

The name is yours. `post:` is conventional for an article and reads well, but
`item:`, `service:` or `person:` are all fine and often clearer. Use the word
that makes the block read like what it is for.