How is stage direction in Pygmalion used to convey the message?

Shaw's stage
directions underscore how poverty-stricken Eliza Doolittle is as the play begins. For example,
when Henry Higgins gives her a good deal of money for her flowers (while not taking any
flowers), she decides to hire a cab to get home. But to show that this is no easy task for a
poor flower seller, Shaw writes the following stage directions, which depict how unusual it is
for a young woman like Eliza to be able to take a taxi:

She sails off to the cab. The driver puts his hand behind him and holds the door firmly
shut against her. Quite understanding his mistrust, she shows him her handful of
money.

In act 2, the stage directions make it clear that
the setting of Henry Higgins's home must show, in multiple ways, how much wealthier he is than
Eliza Doolittle. The instructions are minute and include not only a telephone, a luxury item in
1913, but also candy. The set includes

a telephone and the
telephone directory. The corner beyond, and most of the side wall, is occupied by a grand piano,
with the keyboard at the end furthest from the door, and a bench for the player extending the
full length of the keyboard. On the piano is a dessert dish heaped with fruit and sweets, mostly
chocolates.

All of these stage directions reinforce the
huge class gulf between the main characters.

Shaw uses stage directions, too,
to underline how superficial class differences are, revealing they are based almost entirely on
outward appearance and not on innate differences between people. For example, the stage
directions play up the comedy when Eliza emerges from her bath. When she is clean, her own
father doesn't recognize her:

He [Mr. Doolittle] hurries
to the door, anxious to get away with his booty. When he opens it he is confronted with a dainty
and exquisitely clean young Japanese lady in a simple blue cotton kimono printed cunningly with
small white jasmine blossoms. Mrs. Pearce is with her. He gets out of her way deferentially and
apologizes.

Shaw's stage directions emphasize that vast
class differences exist but also that they are only skin-deep: a point his play means to
make.