ng declaration state</a>,
    then the character encoding used
    <a href="terminology.html#must-requirement" id="must-requirement_xref20">must</a>
    be an
    <a href="syntax.html#ascii-compatible" id="ascii-compatible_xref2">ASCII-compatible character encoding</a>.</p>
    <p>An
    <dfn id="ascii-compatible">ASCII-compatible character encoding</dfn>
    is one that is a superset of US-ASCII (specifically,
    ANSI_X3.4-1968) for bytes in the set 0x09, 0x0A, 0x0C, 0x0D,
    0x20 - 0x22, 0x26, 0x27, 0x2