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There are several national variants of ASCII. As a result, the original ASCII is often referred as *US-ASCII*. The international standard _ISO 646_ \[[ISO/IEC 646-1991|AA. C References#ISO/IEC 646-1991]\] defines a character set similar to US-ASCII, but with code positions corresponding to US-ASCII characters {{@\[\]\{\|\}}} as _national use positions_. It also gives some liberties with characters {{\#$^`\~}}. In _ISO 646_, several national variants of ASCII"\ have been defined, assigning different letters and symbols to the national use positions. Consequently, the characters that appear in those positions, including those in *US-ASCII*, are less portable in international data transfer. Consequently, due to the national variants, some characters are less portable than others--they might be transferred or interpreted incorrectly.