In an app made with mcp_app(trigger = "submit"), input changes wait
until the user presses an apply button. Without one in the UI, the page
adds its own at the bottom; use mcp_submit_button() to choose where it
goes and what it says. The button is disabled until something changes.
See also
Other components:
mcp_input(),
mcp_output(),
mcp_plot(),
mcp_select()
