Each railroad diagram begins with a double right arrow and ends
with a right and left arrow pair. Lines beginning with a single right arrow
are continuation lines. You read a railroad diagram from left to right and
from top to bottom, following the direction of the arrows.
Other conventions used in railroad diagrams are:
Table 1. How to read railroad diagrams
Convention
Meaning
You must specify values A, B,
and C. Required values are shown on the main line of a railroad
diagram.
You may specify value A. Optional values
are shown below the main line of a railroad diagram.
Values A, B, and C are
alternatives, one of which you must specify.
Values A, B, and C are
alternatives, one of which you might specify.
You might specify one or more of the values A, B,
and C. Any required separator for multiple or repeated values
(in this example, the comma (,)) is shown on the arrow.
You might specify value A multiple times.
The separator in this example is optional.
Values A, B, and C are
alternatives, one of which you might specify. If you specify none of the values
shown, the default A (the value shown above the main line)
is used.
Name
The railroad fragment Name is shown separately
from the main railroad diagram.
Punctuation and uppercase values
Specify exactly as shown.
Lowercase values (for example, name)
Supply your own text in place of the name variable.
