This is essentially a way to avoid copying and pasting a bunch of HTML multiple times and then changing a dozen small details in it.
The initial example that they cite in the documentation (which, as I know, you read, but which I quote here for the convenience of links):
<p>
<label>&{'user.name'}</label>
<input type="text" id="user_name" name="user.name" value="${user?.name}" class="${errors.forKey('user.name') ? 'has_error' : ''}">
<span class="error">${errors.forKey('user.name')}</span>
</p>
, , / , &{'user.name'}, user_name, user.name, ${user?.name}, user.name user.name ( ), .
, , .
#{field 'foo'} :
<p>
<label>&{field.name}</label>
<input type="text" id="${field.id}" name="${field.name}" value="${field.value}" class="${field.errorClass}">
<span class="error">${field.error}</span>
</p>
, user.name . / , , : #{field ...}.
, , , , , , , , .. .