tilde syntax

[Ray Andrews <rayandrews@xxxxxxxxxxx>]

    local zsh_case='(#i)'    # insensitive
    # Depending on options: zsh_case=''

    # Where input is some directory name, possibly incomplete and 
matches are looked for:

    subdirs=( $1*(/N) )

    subdirs=( (#i)$1*(/N) )

    subdirs=( $~zsh_case$1*(/N) ) # This works: but tilde must follow 
first dollar sign


The first two seem intuitive,  but the 3d, what does the tilde really 
do?  It has to be there, but one might expect '$zsh_case' to just 
substitute and all's well.  I used to understand this, I remember Roman 
explaining it, but I can't remember and my notes are sketchy.  The tilde 
turns globing into pattern matching, yes? But '(#i)' works if literal, 
it's not mistaken for a glob pattern so why should the use of a variable 
change anything?  Again, pardon, I used to know this.