NOTE: If no buttons are initially visible, then add toolbar button names to the `toolbar_buttons` array of title preset used in `combined_header` block.
# go to any section, that has a toolbar (grid or edit template)
# add visible toolbar button using `a_toolbar.AddButton( new ToolBarMarkup('test_tb1', 'custom tbdata1') );` code (before `a_toolbar.Render();` call)
# confirm, that button is visible
# add hidden toolbar button using `a_toolbar.AddButton( new ToolBarMarkup('test_tb2', 'custom tbdata2', true) );` code (before `a_toolbar.Render();` call)
# confirm, that button is hidden
# dynamically hide initially visible button using `a_toolbar.HideButton('test_tb1');` code (after `a_toolbar.Render();` call)
# confirm, that button is hidden
# dynamically show initially hidden button using `a_toolbar.ShowButton('test_tb2');` code (after `a_toolbar.Render();` call)
# confirm, that button is visible