Ambrosite Next/Previous Post Link PlusbyJ. Michael Ambrosio

IMPORTANT: Make sure you are using the right plugin.

• Next/Previous Post Link Plus is intended for use in single post templates.
• Next/Previous Page Link Plus is intended for use in page templates.

The two plugins have similar sounding, but different, function names. If you mistakenly install the wrong plugin, you will get a “call to undefined function” error. If you want to create next/previous links for your pages, please check out:
https://wordpress.org/extend/plugins/ambrosite-nextprevious-page-link-plus/

IMPORTANT: This plugin is not compatible with PHP 4. If you try to install it on a host running PHP 4, you will get a parse error. WordPress has officially ended support for PHP 4 as of version 3.2, so you should upgrade to PHP 5.2 now. For those who cannot upgrade, you can download the alternate PHP 4 compatible version of the plugin. The only difference with the PHP 4 version is that the %category variable will not work with custom taxonomies.
http://www.ambrosite.com/download/ambrosite-nextprevious-post-link-plus.php4.zip

This plugin creates two new template tags — next_post_link_plus and previous_post_link_plus — which are upgraded versions of the core WordPress next_post_link and previous_post_link template tags. The new tags include all of the functionality of the core tags, plus the following additional options:

• Sort the next/previous post links on columns other than post_date (e.g. alphabetically).
• Sort next/previous links on custom fields (both string and integer sorts are supported).
• Full WordPress 3.3 compatibility, including support for custom post types, custom taxonomies, and post formats.
• Loop around to the first post if there is no next post (and vice versa).
• Retrieve the first/last post, rather than the previous/next post (for First|Previous|Next|Last navigation links).
• Display post thumbnails alongside the links (WordPress 2.9 or higher).
• Truncate the link titles to any length, and display custom text in the tooltip.
• Display the title, date, author, category, and meta value of the next/previous links.
• Specify a custom date format for the %date variable.
• Restrict next/previous links to same category, taxonomy, format, author, custom field value, custom post ID list, or custom category list.
• Exclude categories, custom taxonomies, post formats, or individual post IDs.
• Three category exclusion methods for greater control over the navigation stream.
• Return multiple next/previous links (e.g. the next N links, in an HTML list).
• Return the ID, title, date, href attribute, or post object of the next/previous links, instead of echoing them to the screen.
• Return false if no next/previous link is found, so themes may conditionally display alternate text.
• Works with Post Types Order and other popular post reordering plugins.

Extensive documentation on configuring the plugin may be found here:
http://www.ambrosite.com/plugins/next-previous-post-link-plus-for-wordpress