In "Araby", what does the fence Mangan's sister stands behind symbolize?

Since the boy
idealizes Mangan's sister, the fence may symbolize the division between reality and the
infatuated illusion of the boy in "." 

Or if
Mangan's sister came out on the doorstep to call her brother in tohis tea we watched her from
our shadow peer up and down the street. She was waiting for us [Mangan and the boy], her figure
defined by the light from the half-opened door.  Her brother always teased her before he obeyed
and I stood by the railing looking at her.  Her dress swung as she moved her body and the soft
rope of her hair tossed from side to side.

From the
"sombre" shadows of the houses and the "dark, muddy lanes" of his
neighborhood, the boy see Mangan's sister as an image of Mary, almost saintly with a light
behind yet, yet seductive in her movements and tossing of her hair.  However, he is held at a
distance from her by the "railing."  This symbolic railing, suggestive of a communion
railing in an Irish Catholic church, maintains its motif throughout the story as the boy never
has real contact with Mangan's sister. For instance, when he invites her to the bazaar, she
cannot come because she is going on a religious retreat. 

The boy's other
religious imaginings--carrying parcels on his Saturday shopping, he imagines,

I bore my chalice safely through a throng of foes.  Her name sprang
to my lips at moments in strange prayers and praises...my body was like a harp

However, the relgious "railing" closes these romantic
dreams for the boy as the reality he finds at the bazaar is less than exotic and romantic. After
he arrives late, he hears only petty gossip and the tingling of coins.  Letting his "two
pennies fall against the sixpence" in his pocket, the boy's eyes "burned with anguish
and anger" at his self-deception in his idealized and religious images of Mangan's
sister.