How to use [strings.builder.append]

The reference page of strings.builder.append has its arguments, constraints and declaration.

Appends its value to the closest [strings.builder] scope. The slot requires a value, which can be a constant or an expression, and can only be used inside a [strings.builder] invocation. See the example in the documentation for [strings.builder] above.

Creates a string builder scope. Every [strings.builder.append] invocation found inside it appends its value to the builder, and when the scope ends the value of [strings.builder] becomes the concatenated text. Its children are evaluated as a lambda object, and the slot has no arguments of its own.

strings.builder
   strings.builder.append:"howdy"
   strings.builder.append:" world"
get-value:x:@strings.builder