The double- quotes are not retained as part of the word. The word will consist of exactly the characters between the outer braces, not including the braces themselves. To do this it invokes the Tcl interpreter recursively to process the characters following the open bracket as a Tcl script. There may be any number of command substitutions in a single word. Command substitution is not performed on words enclosed in braces.
Name gives the name of an array variable and index gives the name of an element within that array.
Name must contain only letters, digits, and underscores. Command substitutions, variable substitutions, and backslash substitutions are performed on the characters of index . It may contain any characters whatsoever except for close braces. There may be any number of variable substitutions in a single word. Variable substitution is not performed on words enclosed in braces.