Cell :
    ImportCell
    NamedCell
    Block
    Expression

    _ImportCell     :
    import NamedImports from ModuleSpecifier
    import NamedImports with NamedImports from ModuleSpecifier

    _NamedCell     :
    Identifier = Block
    Identifier = Expression
    FunctionExpression
    ClassExpression

    _Identifier     :
    IdentifierName
    viewof IdentifierName
    mutable IdentifierName