Menu input validation

[Cristovao Verstraeten]

Hi all,

I'm confused in which way I need to implement input validation
for icon fonts markup in a custom menu field.
The basic idea is to validate and restrict the input
for icon font tags only - e.g. glyphicons and font awesome.

I've detailed my question in this github issue along with screenshots and
code:
https://github.com/cristovaov/wp-bootstrap-navwalker/issues/1

Thanks in advance for the help, improvements and your time.
greets,

-Cris.