load(section_id) {
		if (section_id == null)
			L.error('TypeError', 'Section ID required');

		return this.map.data.get(
			this.uciconfig ?? this.section.uciconfig ?? this.map.config,
			this.ucisection ?? section_id,
			this.ucioption ?? this.option);
	}
Load the underlying configuration value.

The default implementation of this method reads and returns the
underlying UCI option value (or the related JavaScript property for
`JSONMap` instances). It may be overridden by user code to load data
from non-standard sources.

@param {string} section_id
The configuration section ID

@throws {TypeError}
Throws a `TypeError` exception when no `section_id` was specified.

@returns {*|Promise<*>}
Returns the configuration value to initialize the option element with.
The return value of this function is filtered through `Promise.resolve()`
so it may return promises if overridden by user code.