url.rewrite-once = (
    "^/label/([-'./+a-z0-9A-Z]+)/$" => "/index.php?page=label&label=$1",
    "^/riddim/([-'./+a-z0-9A-Z]+)/$" => "/index.php?page=riddim&riddim=$1",
    "^/([a-z]+)$" => "/index.php?page=$1",
    "^/(!?pma)([a-z]+)/?$" => "/index.php?page=$1"
)

/riddim/Some+Thing+Here+9.38/ --> works, page is shown
/riddim/Someone's+Stuff+Here/ --> fails, page not found 404 error

RewriteEngine on
RewriteRule ^/label/([-'./+a-z0-9A-Z]+)/$ /index.php?page=label&label=$1
RewriteRule ^/riddim/([-'./+a-z0-9A-Z]+)/$ /index.php?page=riddim&riddim=$1
RewriteRule ^/([a-z]+)$ /index.php?page=$1

"^/riddim/([-'./+a-z%0-9A-Z]+)/$"