# original
if($view_tag =~ m/[^A-Za-z0-9_\-\.]/) {

# corrected
if($view_tag =~ m/^[A-Za-z0-9][\w.-]*/) {

# to anchor the match at the beginning,
# the ^ comes immediately after the first /:
m/^[A-Z ...   

# match the first character
[A-Za-z0-9]

# matching subsequent characters:
[\w.-]*
 
# \w is the same as [A-Za-z0-9_]
# . does not need to be escaped when inside brackets
# put - last inside brackets, otherwise it may indicate a range 
# the quantifier * matches 0 or more instances of the characters