Google quietly announced on Google+ that they made some changes to the IF functions and default values used for ad customizations. Google said "we're making it even easier to customize these ads with IF functions and default values."
IF functions help you customize your ad text based on who’s searching and what device they’re searching on, all without using a feed. For example, if they’re a new customer, you might call out holiday promotions. Or if they’re a returning customer, you might highlight the benefits of your loyalty program. You can also use an IF function to show mobile users customized ad text, such as highlighting your convenient mobile checkout.
Here are more details on IF functions.
Default values can now be used when customizer text can’t be determined from your ad customizer feed or IF function. Say you’re a baking supply retailer promoting professional mixers. You might have an ad headline with an ad customizer set up to show the model name and “mixer.” Starting today, you could set “Professional” as a default value to ensure that even if someone searches for a mixer model that isn’t in your feed, they’ll still see the relevant headline “Professional mixer.” Additionally, by using default values, you no longer need to have an ad without customizers in your ad group.
Here are more details in the help section.
Forum discussion at Google+.