Custom package error ! Missing = inserted for \ifnum

Question

I am trying to create a very basic package for use with a font called HEJI2 (which provides some music symbols to use in-line). My code looks like this:

\ProvidesPackage{heji}[2019/12/9 v1.0]
\RequirePackage{fontspec}[2018/07/30 vv2.6h]

\newfontfamily{\HEfont}{HEJI2.ttf}

\makeatletter
\newcommand*{\fsize}{\dimexpr\f@size pt\relax}
\makeatother

\newcommand{\heji}[2]{\mbox{#1\hspace{0.3mm}\raisebox{0.25\fsize}{\large\HEfont #2}}}

\DeclareOption{accfirst}{
    \renewcommand{\heji}[2]{\mbox{\raisebox{0.25\fsize}{\large\HEfont #2}#1}}
}

\ProcessOptions\relax

\endinput

Using the package seems to work, however when I compile it, I get the following (nonfatal) errors:

! Missing = insterted for \ifnum.
<to be read again>
v
1.4

?
! Missing number, treated as zero.
<to be read again>
v
1.4
?

Not sure what this means exactly. I appear to be able to return through the messages and I get a properly formatted .pdf in the end according to my package specifications. Would appreciate any help! (Compiling with Lualatex)

Answer 1

You can find, for example, in LaTeX2ε for authors (texdoc usrguide), section 3.2 Preamble commands:

That paragraph actually describes the second optional argument to \documentclass, but the date parser is the same. In The LaTeX2ε sources (texdoc source2e), section 68.2 Package name and version there is more or less the same paragraph about \ProvidesPackage.

Firstly, that date format is (still supported but) deprecated, and now the ISO format YYYY-MM-DD should be used instead.

And that requirement is not entirely true. Specifically the day field must be DD, while the other two can even be empty (common sense advises not to ;-), so for example \ProvidesPackage{heji}[1/1/09 v1.0] would've worked. You were unfortunate enough to remove the leading zero from the wrong place ;-)