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Property container

All blocks, whether they are text blocks, image blocks or blocks of any of the other supported types, are wrapped by the responsive API in table <td> elements. In normal circumstances, you do not have to make any changes to such a <td> element, but if you insist, the responsive API allows you to access this element via the container property.

The container property is an advanced nested property inside each block, and can be used to change the styling or even the attributes of the <td>. The container property accepts a JSON object with optional nested css and attributes sub properties. The css and attributes in turn also accept JSON blocks containing the CSS properties or element attributes you want to add to the container.

Container properties

Property Value Description
css object Add custom css to the container element
attributes object Add custom HTML attributes to the container element


Every property that you set in the container css property will be appended to the inline style attribute of the <td> tag. And every attributes property will be set as attribute of the <td> tag. Consider the following JSON example of a button block:

    "from" : "",
    "subject" : "Example container modification",
    "content" : {
        "blocks" : [ {
            "type" : "button",
            "label" : "Responsive",
            "link" : {
                "url" : "",
                "title" : "Go to website"
            "container" : {
                "css" : {
                    "padding" : "20em",
                    "margin" : "2px"
                "attributes" : {
                    "summary" : "This summary is applied to the parent"
        } ]

This would result in the following pseudo HTML

(for the sake of readability, we omitted the default button styling in this example)

<td style="padding: 20em; margin: 2px" summary="This summary is applied to the parent">

Why are table cells used, and not just divs?

The container property allows you to specify custom CSS and attributes for the parent element, which always is a <td> tag. Of course, we've all learned to use tables for displaying tabular data, and use <div> tags to build the lay-out of an HTML design. Not so true with emails!

When building an email lay-out, you have to deal with all sorts of primitive and broken email clients that are not so good at displaying HTML and CSS, and with email clients that strip out stylesheets before the email is rendered. Worst of them all: Gmail (true fact!). One of the many downsides of this whole thing is that having your HTML designs built using divs and floats will make it look like a scrambled egg in almost every email client. Especially in Gmail.

To overcome such problems, email layouts use nested oldschool HTML <table> tags, just like websites did in the 90's. Blocks are not implemented as <div> elements, as you would expect, but <td> tags. An image block, for example, creates an <img> tag, and puts that inside a <td> cell. And this is what the container property inside the JSON block input gives you access to. It allows you to access and modify the <td> tag.

Why you should avoid using these properties

We discourage the use of the container property. We wrote the responsive email API to put an end to all the internal difficulties of building responsive emails. In our opinion, users of the API do not have to deal with specific CSS settings, or with the fact that HTML tables are used. With the responsive email API you can be sure of the fact that any input JSON is turned into a valid responsive email.

The container property completely bypasses this fundamental design principle: the properties are blindly copied from the JSON into the responsive email without any validation. If done wrongly, this could harm your email.