This option should contain the default container/panel alignment this can be a value of "left", "center" or "right". This option can only be used when theme is set to advanced and when the theme_advanced_layout_manager option is set to the value of "RowLayout".
Example of usage of the theme_advanced_containers_default_align option:
tinyMCE.init({
...
theme_advanced_containers_default_align : "left"
});