How can these "Available options", of the Developer Toolbar, be seen?
up arrow and down arrow will scroll through the list of suggestions.
tab will select the current suggestion.
Here is the output from help screenshot
which shows the available options:
In your example using screenshot filename.png --
, --clipboard
is the first matching option:
If you use up arrow and down arrow you will see the other choices.
If you press tab you will see:
How do I use the Developer Toolbar command line?
Using the command line
Like a normal command line, you execute commands by typing them at the prompt and pressing Enter.
As you type, the Developer Toolbar suggests a possible completion to your command.
If there is more than one possible completion, the Up and Down arrow keys cycle through the suggestions. Pressing Tab selects the current suggestion.
Pressing F1 will display all the suggestions in a list, with a summary of what each command will do:
Typing
help <command>
will give you the help for<command>
.The article continues with a list of the possible commands.
Source Developer Toolbar