MaxStringContentLength This quota limits the maximum string size that the XML reader returns. This quota does not limit memory consumption in the XML reader itself, but in the component that is using the reader. For example, when the DataContractSerializer uses a reader secured with MaxStringContentLength, it does not deserialize strings larger than this quota. When using the XmlDictionaryReader class directly, not all methods respect this quota, but only the methods that are specifically designed to read strings, such as the ReadContentAsString method. The Value property on the reader is not affected by this quota, and thus should not be used when the protection this quota provides is necessary.
It limits the maximum size of a string that is returned, either an XML string or a method that returns a string.