Ordinarily, configuration options can be set in either the gallery's XML configuration file or the embedding code.
Options set in the embedding code take precedence over options set in the XML configuration file. (Please see the Setting Config Options support section for details.)

However, galleryWidth and galleryHeight should be set in the embedding code so that the gallery can be sized correctly in the web page as soon as possible (before the configuration file is parsed).
It is noted (in their descriptions in the Configuration Options page) that these options "Must be specified in the embed code.".

They are also included in the XML configuration file so that if the gallery is opened in JuiceboxBuilder for editing, the application can set the correct values in the interface. JuiceboxBuilder reads the gallery's XML configuration file (rather than the embedding code) to find out all the current gallery settings.