ex:proxy = {expression}
 ex:start = {expression}
 ex:end = {expression}
 
 ex:marker = {expression}
 
 ex:topBandIntervalPixels = {number}
 ex:bottomBandIntervalPixels = {number}
 ex:densityFactor = {number}
 
 ex:bubbleWidth = {number in pixels}
 ex:bubbleHeight = {number in pixels}
 
 ex:timelineConstructor = {name of a function}