Squarespace comes preloaded with a large number of blocks that can be added (by users) in pages, posts, and open block fields. All blocks have default system templates that should work for most uses.
Open Block Fields
Open block fields are open areas where users can add blocks. Block fields use the same LayoutEngine grid-based layout system that is used in pages and posts.
Specify open block fields using the Squarespace Block Field tag:
<squarespace:block-field id="blockField1" columns="12"/>
Each block field must have a unique id. The columns attribute can currently be set to 1 or 12. It is usually best to set this to 12, but you can set it to 1 where you want to limit the user to a single column of blocks.
Locking a Layout
A locked layout allows developers to place system blocks on a site without giving front-end users to ability to add additional blocks or change the layout. Front-end users will still have to ability to edit content.
Add lock-layout="true" to any block field to lock the layout.
<squarespace:block-field id="blockField1" columns="12" lock-layout="true"/>
During the beta, we do not support customizing the HTML markup of our system blocks.