Menu Trail By Path sets the active-trail on menu items according to the current url.
For example if you are at yoursite.com/blog/category1/article1
Menu Items with these paths will get the active-trail class on them and expand accordingly.
This is particularly useful if you want a lot of nodes to appear as children of certain nodes / taxonomy term / views / referenced nodes / etc, but do not want to add them all to the menu. eg. hundreds of blog articles.
Menu Trail By Path is best used in conjunction with Pathauto.
This module is similar to Menutrails (D6) and Menu Position (D7), except no configuration is needed. It uses the path URL to determine the active-trail instead of setting rules for each node type. Theoretically, it also works for non-node pages such as taxonomy term and views. Just enable the module to see the results.
8.x-1.x branch is completely rewritten. It should be compatible with any menu.
7.x-2.x branch is completely rewritten. It should be compatible with any menu, including menu_blocks.
Can also handles breadcrumb by path.
NOTE: The 6.x-1.x branch is no longer supported and will not receive further development.
The 6.x-1.x branch only works with primary and secondary links.
To add this functionality for menus other than primary and secondary links, see this issue.