Statement separator

often called by the name of its glyph, Diamond, allows placing multiple statements on a single line. It works both inside a function and directly within the interpreter. Empty statements are generally ignored.

Description
The Statement Separator forces the interpreter to read from left to right. Each separate statement will be read as if on its own line.

A Dictionary of APL states that "expressions using the statement separator can be mimicked by expressions using the verb left. The primary difference is that the separation imposed by   follows the normal rules for order of execution."

Some historical APLs used a right-to-left alternative glyph to achieve the same effect as the left Identity function, as does J. However, and while relevant for J, but not for these historical APLs, this does not allow definition of multiple single-line functions on the same line.
 * APL/700 used a semicolon
 * MCM/70 used a "null operator" jot

Branch takes precedence over statement separators. "If the expression to the right of the branch is not empty, the system goes immediately to the line whose number is the first element in that expression." It is only possible to branch to the first statement on any line.

When displaying an errors message, where the error happened on a line containing statement separators, statements to the right of the position indicated by the error caret have not yet been executed:

Statement separators to the right of a comment  are part of the command are therefore ignored.

Examples
Statements are read from left to right:

Documentation

 * Dyalog
 * APLX
 * NARS2000
 * BQN ( and   are synonymous)