Virtual path can be a relative path (such path is relative to EXE's directory):
1.txt

or a full path
C:\1.txt

it can contain an environment variable (for example, if you would like to use the variable %USERPROFILE%, specify it as <USERPROFILE>):
<USERPROFILE>\some\folder\and\one\more\1.txt

also variables <CurDir> and <ExeDir> are available:
<ExeDir>\1.txt
<CurDir>\tratata\SomeDLL.dll

Read more about supported variables here: Variables