6.1.2.5.2 Restrictions for Code Extension

⎯ As code elements G0 and G1 always have shift status, Locking Shifts (SI, SO) are not required and shall not be used.

⎯ As code elements G2 and G3 are not used, Single Shifts (SS2 and SS3) cannot be used.

⎯ Only the ESC sequences specified in PS 3.3 shall be used to activate Code Elements.