Section of drupal_build_form() documentation listing (some) common
properties (more need to be added):

 * @return
 *   The built and processed form array. This function may also perform a
 *   redirect and hence may not return at all, depending upon the $form_state
 *   flags that were set. Form arrays are like generic renderable arrays (see
 *   drupal_render() for details), except that their #type property is 'form',
 *   and their children are form elements. Besides the common renderable array
 *   properties listed in drupal_render(), the following properties are common
 *   to all form elements:
 *   @form_property_all #disabled
 *     If TRUE, the form element is disabled (greyed out).
 *   @form_property_all #required
 *     If TRUE, the form element is required to have a value to accept
 *     submission.
 *   @form_property_all #name
 *     The HTML name of the form element.
 *   @form_property_all #process
 *     An array of functions called to process form submissions. See
 *     form_builder() for details.
 *   @form_property_all #value_callback
 *     A function that maps user input to the element's #value property. See
 *     form_builder() for details.
 *   The following properties are used by some (but not all) form elements:
 *   @form_property #description
 *     The translated description of the form element, typically displayed
 *     below the input field.
 *   @form_property #title
 *     The translated title of the form element.
 *   @form_property #multiple
 *     If TRUE, multiple selections are allowed for this form element.
 *   @form_property #options
 *     An array of options for this form element. The array elements are the
 *     displayed option values, and the keys (if provided) are the returned
 *     values for each option (if there are no keys, the array values are used).


drupal_render() documentation:

/**
 * Renders HTML given a structured array tree.
 *
 * Recursively iterates over each of the array elements, generating HTML code.
 *
 * @param $elements
 *   The structured array ("renderable array" or "element") describing the data
 *   to be rendered. Renderable arrays have two kinds of key/value pairs:
 *   properties and children. Properties have keys starting with '#', and their
 *   values influence how the array will be rendered. Children are all array
 *   elements whose keys do not start with a '#'. Their values are themselves
 *   renderable arrays, which will be rendered during the rendering of the
 *   parent array. The markup provided by the children is typically inserted
 *   into the markup generated by the parent array. The following properties
 *   are common to all renderable arrays:
 *   @render_property_all #type
 *     The type of element to render, as defined in a hook_element_info()
 *     implementation. Default property values for this element type from
 *     hook_element_info() are added to the $elements array.
 *   @render_proprety_all #pre_render
 *     An array of functions to call, in order, before theming the element.
 *   @render_property_all #theme
 *     If set, the name of the theme hook to be used to render this element and
 *     possibly its children (if any). If #theme is not set (or returns empty),
 *     and the element has children, the default theming is to render each of
 *     the children (by calling drupal_render() recursively) and concatenate.
 *   @render_property_all #theme_wrappers
 *     Array of theme hooks to be called, in order, after the #theme function
 *     is finished, to add additional markup around the rendered element. This
 *     allows the #theme property to be overridden, while still supplying
 *     required markup.
 *   @render_property_all #cache
 *     To use caching to improve performance, set the #cache property to an
 *     associative array with one or several of the following array elements:
 *     - keys: An array of one or more keys that identify the element. If set,
 *       the cache ID is created automatically from these keys. See
 *       drupal_render_cid_create().
 *     - granularity (optional): Define the cache granularity using bitwise OR
 *       combinations of the cache granularity constants, e.g.
 *       DRUPAL_CACHE_PER_USER to cache for each user separately or
 *       DRUPAL_CACHE_PER_PAGE | DRUPAL_CACHE_PER_ROLE to cache separately for
 *       each page and role. If not specified, the element is cached globally
 *       for each theme and language.
 *    - cid: Specify the cache ID directly. Either 'keys' or 'cid' is required.
 *      If 'cid' is set, 'keys' and 'granularity' are ignored. Use only if you
 *      have special requirements.
 *    - expire: Set to one of the cache lifetime constants.
 *    - bin: Specify a cache bin to cache the element in. Defaults to 'cache'.
 *   @render_property_all #access
 *     TRUE if the user has access to see this element; FALSE otherwise. If set
 *     and FALSE, nothing is returned.
 *   @render_property_all #weight
 *     Numeric value indicating the order of children within a renderable array.
 *     Children with lower values appear before those with higher values; can
 *     be negative.
 *   The following properties are used by one or more types of renderable
 *   arrays, but not all types:
 *   @render_property #markup
 *      HTML markup for this element. If #type has not been set and #markup is
 *      present, #type will be set to 'markup'.
 *   @render_property #attributes
 *      Attributes to add to the outer HTML tag of the element.
 *   The following internal-use properties are common to all renderable arrays:
 *   @render_property_internal #printed
 *     During rendering, this function flags each element with a #printed
 *     status to indicate that the element and its children have already been
 *     rendered. If an already-rendered element is passed in, nothing is
 *     returned from this function.
 *   @render_property_internal #sorted
 *     During rendering, children are sorted using uasort(), and the #sorted
 *     property is set. Since this is expensive, when calling this function
 *     with already-sorted elements, set #sorted to TRUE to avoid sorting a
 *     second time.
 *   @render_property_internal #children
 *     The results of the theming are stored in this property during rendering.
 *     See #theme and #theme_wrappers properties.
 *
 * @return
 *   The rendered HTML.
 */
function drupal_render(&$elements) {


Sample render element documentation:

/**
 * Returns HTML for a generic HTML tag with attributes.
 *
 * @render_element html_tag
 *
 * @param $variables
 *   An associative array containing:
 *   - element: A renderable array describing the tag.
 *     @properties
 *       #tag, #attributes, #value, #value_prefix, #value_suffix
 *     @render_property_specific #tag
 *       The tag name to output. Typical tags added to the HTML HEAD:
 *       - meta: To provide meta information, such as a page refresh.
 *       - link: To refer to stylesheets and other contextual information.
 *       - script: To load JavaScript.
 *     @render_property_specific #value
 *       (optional) A string containing tag content, such as inline CSS.
 *     @render_property_specific #value_prefix
 *       (optional) A string to prepend to #value, e.g. a CDATA wrapper prefix.
 *     @render_property_specific #value_suffix
 *       (optional) A string to append to #value, e.g. a CDATA wrapper suffix.
 */
function theme_html_tag($variables) {

/**
 * Returns HTML for a select form element.
 *
 * @form_element select
 *
 * It is possible to group options together; to do this, change the format of
 * $options to an associative array in which the keys are group labels, and the
 * values are associative arrays in the normal $options format.
 *
 * @param $variables
 *   An associative array containing:
 *   - element: A form element array containing the properties of the element.
 *     @properties
 *       #title, #value, #options, #description, #extra, #multiple, #attributes,
 *       #options, #size.
 *     @form_property_specific #size
 *       The width of the select element.
 *
 * @ingroup themeable
 */
function theme_select($variables) {