The AT Commands have standardized syntax rules.
Words enclosed in <angle brackets> are references to syntactical elements. Words enclosed in [square brackets] represent optional items which may be left out from the command line at the specified point. The brackets are not used when the words appear in the command line.
<CR>, <LF>, and terminating NUL are
allowed in an AT command sent by an application, but are not mandatory when using an interface
where both the command string and length of command string are provided.
All standard AT commands for controlling a phone or a modem or managing the SMS feature begin with a plus sign (+), whereas Nordic-proprietary commands begin with a percent sign (%).
A string type parameter input should be enclosed between quotation marks ("").