@component({
 selector: 'x', 
 template: 'Heya, @p@'
 interpolation: ['@', '@']
})
export class X {
 p = 'wassup!'
}

private _consumeIncompleteBlock(token: IncompleteBlockOpenToken) {
    const parameters: html.BlockParameter[] = [];

    while (this._peek.type === TokenType.BLOCK_PARAMETER) {
      const paramToken = this._advance<BlockParameterToken>();
      parameters.push(new html.BlockParameter(paramToken.parts[0], paramToken.sourceSpan));
    }

    const end = this._peek.sourceSpan.fullStart;
    const span = new ParseSourceSpan(token.sourceSpan.start, end, token.sourceSpan.fullStart);
    // Create a separate `startSpan` because `span` will be modified when there is an `end` span.
    const startSpan = new ParseSourceSpan(token.sourceSpan.start, end, token.sourceSpan.fullStart);
    const block = new html.Block(token.parts[0], parameters, [], span, token.sourceSpan, startSpan);
    this._pushContainer(block, false);

    // Incomplete blocks don't have children so we close them immediately and report an error.
    this._popContainer(null, html.Block, null);

    this.errors.push(
      TreeError.create(
        token.parts[0],
        span,
        `Incomplete block "${token.parts[0]}". If you meant to write the @ character, ` +
          `you should use the "&#64;" HTML entity instead.`,
      ),
    );
  }

const UNUSABLE_INTERPOLATION_REGEXPS = [
    /@/, //reserved control flow syntax <------------------------ Addition
    /^\s*$/, // empty
    /[<>]/, // html tag
    /^[{}]$/, // i18n expansion
    /&(#|[a-z])/i, // character reference,
    /^\/\//, // comment
];
function assertInterpolationSymbols(identifier, value) {
    if (value != null && !(Array.isArray(value) && value.length == 2)) {
        throw new Error(`Expected '${identifier}' to be an array, [start, end].`);
    }
    else if (value != null) {
        const start = value[0];
        const end = value[1];
        // Check for unusable interpolation symbols
        UNUSABLE_INTERPOLATION_REGEXPS.forEach((regexp) => {
            if (regexp.test(start) || regexp.test(end)) {
                throw new Error(`['${start}', '${end}'] contains unusable interpolation symbol.`);
            }
        });
    }
}