I think programming languages should implement placeholder syntax as a formal part of the language.

For instance, you could say <#EXPR#> is an expression. Then, when people give code examples where they leave a placeholder for an expression, using <#EXPR#> is going to be parseable and syntax-highlighted, instead of only sometimes being usable.

For instance:

<#TYPE#> get_<#IDPART#>(<#FNARGS#>) {
<#ID#> = 7;
}