Symbols are defined by the pergola.symbols library object.
A symbol is an array of one or more elements with their paint and geometrical attributes. When using a symbol you can override its attributes or define new ones, using SVG attributes vocabulary.
You can attach a symbol to objects like buttons, tools, etc., or use it as standalone to create icons by invoking the pergola.symbol() utility function.
Learn more in the SYMBOLS library section of the Tutorial.