Mutations don't produce new features

Claim

Mutations only vary traits that are already there. They don't produce anything new.

Most changes in evolution do not involve the creation of anything new. Horses, for example, evolved over the past 50 million years entirely via the modification of features, yet the changes that resulted were profound.
No one asserts that mutations produce new features all at once. What evolutionary theory asserts is that new features are built primarily from gradual modifications of old ones.
Creationists who make this claim fail to notice that the ability to secrete the enzyme nylonase has evolved no less than three times among 3 different bacteria strains in laboratories within the last 20 years.
Creationists who use this claim refuse to define exactly what a "new feature" would be. This way, they can dismiss all examples of "new features" shown to them as being merely "old features" that had been modified. Without a specific definition for what exactly constitutes a "new feature," this term is a useless, meaningless hyperbole.
It has been demonstrated that drug resistance in bacteria is the result of mutation and not adaptation.[1]
A simple mutation would have been sufficient to evolve feather-like keratin genes from scale keratin genes.
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Straw Man (no one asserts that mutations produce new features all at once)
Begging the Question (assumes mutations can't produce new features in order to prove that it can't happen)
Moving Goalpost Syndrome (all examples of actual "new features" are disqualified and or ignored)

Mark Isaak's page for this claim [2]
Mark Isaak's page on mutations create variation [3]
CreationWiki's comments [4]
Musgrave, Ian, Steven Pirie-Shepherd, and Douglas Theobald, 2003. Apolipoprotein AI Mutations and Information. [5]
Max, Edward E., 1999. The Evolution of Improved Fitness By Random Mutation Plus Selection. [6]
Thomas, Dave, n.d. Evolution and Information: The Nylon Bug. [7]