hasSystemFeature() {
			const ft = sysFeatures[arguments[0]];

			if (arguments.length == 2)
				return this.isObject(ft) ? ft[arguments[1]] : null;

			return (ft != null && ft != false);
		}
Test whether a particular system feature is available, such as
hostapd SAE support or an installed firewall. The features are
queried once at the beginning of the LuCI session and cached in
`SessionStorage` throughout the lifetime of the associated tab or
browser window.

@instance
@memberof LuCI

@param {string} feature
The feature to test. For detailed list of known feature flags,
see `/modules/luci-base/root/usr/share/rpcd/ucode/luci`.

@param {string} [subfeature]
Some feature classes like `hostapd` provide sub-feature flags,
such as `sae` or `11w` support. The `subfeature` argument can
be used to query these.

@return {boolean|null}
Return `true` if the queried feature (and sub-feature) is available
or `false` if the requested feature isn't present or known.
Return `null` when a sub-feature was queried for a feature which
has no sub-features.