defines a placeholder within a template where customized content can be inserted into.
Consider the example below, which are 16 cubes in a 4 by 4 grid layout:
By replacingwith , we turn this layout into a reusable template where we can create grid of our own customized object instead of the cube.
Here, we modify the previous example to produce a grid of pins with a rounded head, each is modeled as a dome above a cylinder.
Named content tags
Content tags can be individually named to take on distinct roles.
Let's look at the example below, which is a sandwich model consisting of a top,
a middle, and a bottom layer. In between layers are flat cylinders colored in yellow.
Each layer is defined as a content holder. Then, when
<sandwidth> is used,
we can individually model what goes into each layer, which is represented by
the children tags
<bottom> respectively. Inside
each child tag, we add a dome, a cube, and a sphere respectively, and color
them in brown.