$ mono context.exe -f
# Parsed -f; Value=<null>; Index=0
f=<null>
n=-1
s=<null>

$ mono context.exe -n
context: Missing required value for option '-n'.

$ mono context.exe -s
# Parsed -s; Value=<null>; Index=0
f=<null>
n=-1
s=<null>

$ mono context.exe -f=invalid
# Parsed -f; Value=invalid; Index=0
context: Could not convert string `invalid' to type Foo for option `-f'.

$ mono context.exe -n invalid
# Parsed -n; Value=invalid; Index=1
context: Could not convert string `invalid' to type Int32 for option `-n'.

$ mono context.exe -s=
# Parsed -s; Value=; Index=0
f=<null>
n=-1
s=

$ mono context.exe -f=A --n=42 /s=fourty-two
# Parsed -f; Value=A; Index=0
# Parsed --n; Value=42; Index=1
# Parsed /s; Value=fourty-two; Index=2
f=A
n=42
s=fourty-two