Understanding Initialization

Timeline.createBandInfo() fills in default settings, for constructing a band in a timeline. Defaults can be changed using parms. What Timeline.createBandInfo() does is something like this (in pseudo-code):

 Timeline.createBandInfo = function(params) {
   return {
     width:          params.width,
     eventSource:    params.eventSource, //(or null by default)
     timeZone:       params.timeZone, //offset from GMT (default is 0)
     ether:          new Timeline.LinearEther({
                       interval: f(params.intervalUnit), //the number of milliseconds in params.intervalUnit 
                       pixelsPerInterval: params.intervalPixels,
                       centersOn: params.date  //or the current date by defaul
                     }),
     etherPainter:   new Timeline.GregorianEtherPainter({
                       unit:      params.intervalUnit,
                       theme:     params.theme, //or the default theme
                     }),
     eventPainter:   new Timeline.DurationEventPainter({
                       showText:  params.showEventText, //or true by default
                       theme:     params.theme, //or the default theme...same theme above
                       trackHeight: params.trackHeight, //orr the default track height in the theme
                       trackGap:    params.trackHeight, //or the default track gap in the theme
                       layout:     new Timeline.StaticTrackBasedLayout({
                                      eventSource: //same as the same eventSource above
                                      ether:       //same ether above
                                      showText:    //same showText value above
                                      theme:       //same theme above
                                    })
                     })
   }
 };

In other words, Timeline.createBandInfo() takes an object whose fields store initialization settings and returns yet another object whose fields stores initialization settings that Timeline.create() can understand.

Timeline.createBandInfo() does the work of routing each initialization setting that you give it to the appropriate place(s). For example, params.intervalUnit is referenced twice above, once to construct an ether and once to construct an ether painter. Whatever default setting that Timeline.createBandInfo() doesn't provide is provided by the theme.