Post meta is easily one of the most useful features in WordPress from a developer’s perspective.  Adding custom content to a post provides the ability to accomplish countless goals quickly and easily.

Sometimes, it makes sense to give the user access to a post meta field – for example, if they need to add a thumbnail url to a post, they’re probably going to need to access to those post meta fields.  Other times, having the post meta field visible is only likely to confuse the visitor.  One (extremely popular) place that I’ve seen this is the All in One SEO Plugin.  All in One SEO is wildly popular, and does what it claims well.  It provides a few extra fields, and a nice, easy to use interface to get at them.  Here’s what it looks like when you get started:

Fantastic.  It’s attractive, easy to use, and works well.  So we save our post, and then later on, we go back to edit the meta description.  Here’s what we get:

At this point, its pretty clear what’s going on if you understand the inner workings of WordPress – AIOSEO has saved our values to custom fields, so now they’re showing up there.  However, most users dont understand, or even care about how AIOSEO works, or what custom fields are.  All they know is that strange stuff is showing up, and they’re not sure where to edit their meta keywords, because they’re showing up in 2 places.  Most people have the gumption to just change one and see what happens – but there will always be users who get scared and decide they want to email you about the issue, or worse, just uninstall the plugin and move on.

Underscores to the Rescue

The WordPress developers, fortunately, thought of this.  In fact, they store all kinds of stuff that they don’t want the user to see in custom fields – things like the last time the post was edited, who is currently editing it, and a few others.  A quick look at the database, reveals this:Notice a trend?  The mysterious custom field key values are prepended with an underscore.  Give it a try – enter a new custom field from the edit-post page, and enter a name that starts with an underscore – like _thumbnail, or _meta_keywords.  Hit “Add Custom Field”, and it disappears – but if you check the database, its right where it should be.

Now get out there and start hiding things from your users!