Note: this chapter is not yet complete!
Nodes are Drupal's most basic content unit. Traditionally in Drupal every type of content like a page or blog post is a node, although in Drupal 7 it is not strictly necessary to use nodes when something like a Views Page or an Entity record might be more suitable. Modules can define their own node types as well.
Here are the default properties of Drupal 7 node objects from the official documentation. Generally all these properties are available in the theme layer when working with node displays:
| $node->nid | Node ID. |
| $node->vid | The revision ID of the current version of this node. |
| $node->type | Type of node (e.g. book, page, forum), which is also the entity bundle. |
| $node->language | The default language for this node. |
| $node->title | Page (or, more accurately, node) title. |
| $node->uid | User ID of node creator. |
| $node->status | unpublished/published (NODE_NOT_PUBLISHED | NODE_PUBLISHED). |
| $node->created | UNIX timestamp of node creation date. |
| $node->changed | UNIX timestamp of last time node was changed. |
| $node->comment | Whether comments are allowed on this node (COMMENT_NODE_HIDDEN | COMMENT_NODE_CLOSED | COMMENT_NODE_OPEN) |
| $node->promote | Promoted to front page (NODE_NOT_PROMOTED | NODE_PROMOTED). |
| $node->sticky | Sticky (NODE_NOT_STICKY | NODE_STICKY). |
| $node->tnid | The node ID of the translation source (or parent, if node is a translation). |
| $node->translate | Does the translation need to be updated (0|1)? |
| $node->revision_uid | The user ID of the user who created the current revision. |
| $node->body | Array. Body content of node. Long text field with summary. Note: Don't assume that this field will exist, as it is possible to remove it via Manage Fields on each content type. Similarly, modules that define a custom node content type may not even attach a body in the first place. |
| $node->log | Message left by the creator of this revision, explaining the changes. |
| $node->revision_timestamp | Unix timestamp showing when current revision was created. |
| $node->name | Username of node creator. |
| $node->picture | User avatar of the node creator. |
| $node->cid | CID of last comment? |
| $node->last_comment_timestamp | Timestamp of last comment (Unix Epoch C). |
| $node->last_comment_name | Name of last comment author |
| $node->last_comment_uid | UID of last comment author. |
| $node->comment_count | Number of comments made on node. |
| $node->data | Serialized string of data associated with the node. |
| $node->rdf_mapping | W3C standard to describe structured data. See http://api.drupal.org/api/drupal/modules!rdf!rdf.module/group/rdf/7 |
To create a new property on a node programmatically, the Entity API module can be very helpful. The hook_entity_property_info hook lets you set up the metadata properties. The entity_metadata_node_entity_property_info function implements hook_entity_property_info() on top of the node module, for default node property definitions.
You can find more documentation in the Entity API handbooks. Also check the README and the provided API docs in entity.api.php.