/**
 * @param {('rect'|'circle'|'ellipse')} shapeType - The allowed type of the shape
 */

References:

• http://stackoverflow.com/questions/19093935/how-to-document-a-string-type-in-jsdoc-with-limited-possible-values
• Enum of strings jsdoc/jsdoc#629
• A method of documenting a predefined set of parameter values jsdoc/jsdoc#1065

This is necessary for #18 to document such things as the valid values for @kind.