# Lexical analysis
In the lexical analysis step, the expl3 analysis tool converts the expl3 parts of the input files into a list of `\TeX`{=tex} tokens.

## “Weird” and “Do not use” argument specifiers {.w}
Some control sequence tokens correspond to functions with `w` (weird) or `D` (do not use) argument specifiers.

``` tex
\cs_new:Npn
  \show_until_if:w  % warning on this line
  #1 \if:w  % warning on this line
  { \tl_show:n {#1} }
\show_until_if:w  % warning on this line
  \tex_if:D  % warning on this line
  \if_charcode:w  % warning on this line
  \if:w  % warning on this line
```

The above example has been taken from @latexteam2024interfaces [Chapter 24].

## Unknown argument specifiers {.e}
Some control sequence tokens correspond to functions with unknown argument specifiers. [@latexteam2024interfaces, Section 1.1]

``` tex
\cs_new:Nn
  \example:bar  % error on this line
  { foo }
  { bar }
  { baz }
```

## Deprecated control sequences {.w}
Some control sequence tokens correspond to deprecated expl3 control sequences from `l3obsolete.txt` [@josephwright2024obsolete].
<!-- vi "$(texdoc -Il l3obsolete.txt | sed -r 's/\s*[0-9]+\s*//')" -->

``` tex
\str_lower_case:n  % warning on this line
  { FOO BAR }
```

## Removed control sequences {.e}
Some control sequence tokens correspond to removed expl3 control sequences from `l3obsolete.txt` [@josephwright2024obsolete].
<!-- vi "$(texdoc -Il l3obsolete.txt | sed -r 's/\s*[0-9]+\s*//')" -->

``` tex
\msg_log:n  % error on this line
  {
    Foo~bar~
    \c_one_thousand  % error on this line
  }
```

## Missing stylistic whitespaces {.s}
Some control sequences and curly braces are not surrounded by whitespaces [@latexteam2024programming, Section 6] [@latexteam2024style, Section 3].

``` tex
\cs_new:Npn \foo_bar:Nn #1#2
{
  \cs_if_exist:NTF#1  % warning on this line
    { \__foo_bar:n {#2} }
    { \__foo_bar:nn{#2}{literal} }  % warning on this line
}
```

## Malformed function name {.s}
Some function have names that are not in the format `\texttt{\textbackslash\meta{module}\_\meta{description}:\meta{arg-spec}}`{=tex} [@latexteam2024programming, Section 3.2].

``` tex
\cs_new:Nn
  \description:  % warning on this line
  { foo }
```

``` tex
\cs_new:Nn
  \module__description:  % warning on this line
  { foo }
```

``` tex
\cs_new:Nn
  \_module_description:  % warning on this line
  { foo }
```

``` tex
\cs_new:Nn
  \__module_description:
  { foo }
```

## Malformed variable or constant name {.s}
Some expl3 variables and constants have names that are not in the format `\texttt{\textbackslash\meta{scope}\_\meta{module}\_\meta{description}\_\meta{type}}`{=tex} [@latexteam2024programming, Section 3.2], where the `\meta{module}`{=tex} part is optional.

``` tex
\tl_new:Nn
  \g_description_box  % warning on this line
\tl_new:Nn
  \l__description_box  % warning on this line
\tl_const:Nn
  \c_description  % warning on this line
  { foo }
```

``` tex
\tl_new:Nn
  \g_module_description_box
\tl_new:Nn
  \l_module_description_box
\tl_const:Nn
  \c__module_description_box
  { foo }
```

An exception is made for scratch variables [@latexteam2024interfaces, Section 1.1.1]:

``` tex
\tl_use:N
  \l_tmpa_tl
\int_use:N
  \l_tmpb_int
\str_use:N
  \l_tmpa_str
```

## Malformed quark or scan mark name {.s}
Some expl3 quarks and scan marks have names that do not start with `\q_` and `\s_`, respectively [@latexteam2024programming, Chapter 19].

``` tex
\quark_new:N
  \foo_bar  % error on this line
```

``` tex
\quark_new:N
  \q_foo_bar
```

``` tex
\scan_new:N
  \foo_bar  % error on this line
```

``` tex
\scan_new:N
  \s_foo_bar
```

## Too many closing braces {.e}
An expl3 part of the input file contains too many closing braces.

``` tex
\tl_new:N
  \g_example_tl
\tl_gset:Nn
  \g_example_tl
  { Hello,~ } }  % error on this line
```