Computer readable media and methods are associated with a software development tool that is useful when authoring programs that generate documents, such as markup language documents. In one respect, the invention is a computer readable medium on which is embedded computer software. The software comprises a base class, an inline class and a container class. The base class defines a parent-child relationship by which a child object is stored within the storage space of its parent object. The inline class is an extension of the base class, wherein a member of the inline class is permitted to be a child object but prohibited from being a parent object. The container class is an extension of the base class, wherein a member of the container class is permitted to be a child object and/or a parent object. A well-formed document can be modeled in software using members of the inline and/or container classes. In another respect, the invention is a method of using the a set of classes to develop a document-producing program. The set of classes comprises the base class, inline class and container class. In yet another respect, the invention is a document-producing program produced by the preceding method.