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I see this all the time: object literals declared such that some keys are surrounded with quotes and others are not. An example from jQuery 1.4.2: jQuery.props = { "for": "htmlFor", "class": "className", readonly: "readOnly", maxlength: "maxLength", cellspacing: "cellSpacing", rowspan: "rowSpan", colspan: "colSpan", tabindex: "tabIndex", usemap: "useMap", frameborder: "frameBorder" }; What is the significance of wrapping the first two property keys ( for and class ) with quotes, while leaving the others quote-less? Are there any differences at all? I've been poking around the ECMAScript 5 specification ; all I've been able to find is [ Note 6 of Section 15.12.3, emphasis mine ]: NOTE 6 An object is rendered as an opening left brace followed by zero or more properties, separated with commas, closed with a right brace. A property is a quoted String representing the key or property name , a colon, and then the stringified property value. An array is rendered as an opening left bracket followed by zero or more values, separated with commas, closed with a right bracket. However, this refers only to the stringification of JSON.

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