is a textual representation of containers that uses parentheses as delimiting tokens to stand in place of surrounding containers. page 
In the Image page , configurations are illustrated on each line, while the temporal evolution of applying transformations to parens configurations is shown as the stepwise progression of changed configurations going down the page.
A parens demonstration shows an Animation, with time spread in the vertical direction and with some parallelism suppressed. Iconic forms can be illustrated using linear text, using planar enclosures, or using solid objects.
For example, the binary number 6 expressed […] in one, two, and three dimensions.
One-dimensional parens configurations represent the application of rules by changing the sequence of symbols in the textual expression.
Two-dimensional container configurations express change by Animation.
Three-dimensional block configurations are intended to express change as physical activities.
Thus iconic transformation rules can be expressed statically as textual rewrites, dynamically as shifting boundaries, and physically as the reorganization of concrete objects.
The diversity of iconic representations is described more fully on the Varieties page.