'That I can understand Neal, but what about outdoors in a landscape situation or where one can't walk up and get in the shadows?'

Then one imitates the shadows, or finds similar lighting conditions, taking great care not to measure in too deep a shadow.

The caveat is that haze cannot really be taken into account, except by operator intervention. Obviously, haze (aerial perspective) lightens the distant shadow values to a degree that can't be measured by an incident meter.

Though the incident system is referred to by many as the BTZS system, Minor White mentioned it in his 1967 Zone System Manual and it may not have been radical then, for all I know.