# What is the purpose of \protect? [duplicate]

Possible Duplicate:
What is the difference between Fragile and Robust commands?

I've never understood the purpose of the command `\protect`? When and why should it be used?

To understand how to use `\protect` you need to understand the concept of fragile commands and to understand this concept, you need to understand what a moving argument is. Some commands called fragile commands causes an error when they use a moving argument. It's a command that expands into illegal TeX code during the save process. Some arguments are called moving arguments because they may be "moved" to other places in the document. A fragile command that appears in a moving argument must be preceded by a `\protect` command. For example,

• sectioning commands
• arguments of `\caption` commands
• commands that produce page headings

An example :

``````\caption{Beautiful picture from \protect \citeauthor{allan}
\protect \shortcite{allan}}
``````
• "[A fragile command is a command that] expands into illegal TeX code during the save process." - What does this mean? What is the "save" process? How does a command that expands into illegal TeX successfully compile? Are there circumstances wherein a so-called "fragile command" expands into legal TeX? – Jake Aug 5 '16 at 6:17
• I'm with @Jake here. While the answer technically answers the question, it leaves open a lot of questions. However this question is a duplicate anyway and the answer on the other question as linked on top is far more detailed. – Sunday Dec 7 '17 at 10:18