<container>
This is the simplest form to group the data for improving its visualization.
On the resulting window, in addition to the inputs there will be the following set of buttons: 
It can contain the following fields: <value>, <container>, <condition>, <function>, <dependencies>
The parameters are as follows,
n - Name used to reference the field, especially when writing the .dat file.
pn - Label that will be visualized by the user. It can be translated.
icon - It allows to put an image in .png format in the data tree. The image should be stored inside the images folder of the problem type.
help - It displays a pop-up window of help information related to the task the user is performing.
help_image - declare an image filename with the image to be shown below the help text. The file must be located inside a problemtype folder named 'images' and the help attribute is required to use help_image
e.g.
help= "my help text" help_image= "laminates.png".
state - Specifies one of two states for the field: normal, or hidden. Note that hidden <container> field can be used for storing hidden values, that you do not want to show in the user interface. It also permits to handle a Tcl function, by means of square brackets.
update_proc - It calls a Tcl procedure, when clicking on the 'Ok' button in the window. (must not add square brackets in this case). The Tcl procedure must be defined in a <proc> node of the spd
actualize_tree - Itupdates the information in the whole data tree, and automatically refresh data shown in the user interface. It is a boolean value as a 1 or 0 that indicates if it is activated or deactivated. If the data source is changed, such as new fields have been added or data values and field have been modified, all the user interface will reflect those changes. Furthermore, all the TCL procedures defined in the data tree will be called and the whole data tree will be refreshed. Therefore, this instruction must be carried out only when necessary.
actualize - This only updates a specified field in data tree. Note that only this specified field will be refreshed in the user interface, and not the whole data tree. It is a boolean value as a 1 or 0 that indicates if it is activated or deactivated.
del_cancel_button - It is a boolean value as a 1 or 0 that indicates if the cancel button is removed (1) or not (0). On the resulting window there will be only the 'OK' button, as follows, 
Fields to allow customize tree contextual menu:
addcontextualmenu -To add a new option to the menu. Expects a Tcl list of items, each item with subitems "icon text tcl_command"
replacecontextualmenu -To replace a menu option. Expects a Tcl list of items, each item with subitems "old_text icon text tcl_command"
removecontextualmenu -To remove a menu options. Expects a Tcl list of items, each item with subitems "old_text"
Example:
<container n='general_data' pn='General data' icon='general'> <value n='max_iterations' pn='Maximum iterations' value='1e3' help='limit of iterations for iterative solver'/> <value n='stop_tolerance' pn='Stop tolerance' value='1e-8'/> </container>
Example: (customize contextual menu)
<blockdata n="Simulation_type" pn="Simulation data" icon="[icon_simtype]" addcontextualmenu="{advanced-16 {Add option 1} CompassFEM::Test} {advanced-16 {Add option 2} CompassFEM::Test}" replacecontextualmenu="{{Edit} advanced-16 {Edit mod.} CompassFEM::Test} {{View this} advanced-16 {View this mod.} CompassFEM::Test_mod}" removecontextualmenu="{View this} {Edit}"</blockdata>