Here is a list of all documented variables with links to the struct/union documentation for each field:

abi_version : rgbx_manifest
accel : rgbx_inputs
audio_band_energy : rgbx_inputs
audio_beat : rgbx_inputs
audio_display_bucket : rgbx_inputs
boolean : rgbx_param_default
buttons_pressed : rgbx_inputs
color : rgbx_param_default
default_value : rgbx_param_desc
dt_ms : rgbx_inputs
f32 : rgbx_param_default
gyro : rgbx_inputs
height : rgbx_manifest
name : rgbx_manifest, rgbx_param_desc
param_count : rgbx_manifest
param_strings : rgbx_inputs
params : rgbx_inputs, rgbx_manifest
str : rgbx_param_default
type : rgbx_param_desc
u32 : rgbx_param_default
width : rgbx_manifest