# How to Enter an Identifier

An identifier is a name which starts with a letter and contains only letters and digits. The list of allowed characters is specified in config file [IDA.CFG](https://docs.hex-rays.com/9.0sp1/user-guide/configuration/configuration-files). All names are case-sensitive.

Maximal length of a name is specified in the configuration file too:

```
        MAX_NAME_LENGTH=120     // Maximal length of new names
```

Default is 120.

Some assemblers have a shorter name length limit, beware!

IDA will warn you if you enter an illegal name.