Function substitute_printfile 

pub fn substitute_printfile(template: &str, data: &PrintfileData<'_>) -> String

Perform original hypermail printfile()-style %x substitution on a template string.

Supported escapes:

• %% → %
• \n → newline, \t → tab
• %~ → output directory
• %a → other-archives URL
• %b → about-archive URL
• %c → charset <meta> tag
• %d → human-readable date string for display (plain text, no markup)
• %D → date <meta name="Date"> tag (message pages only)
• %e → author email address
• %f → filename
• %g → current date/time string
• %G → two-letter language code
• %h → hypermail homepage URL
• %i → Message-ID
• %j → localized “Subject:” label (e.g., “Betreff:” in German, “Θέμα:” in Greek)
• %k → localized “Date:” label (e.g., “Datum:” in German, “Ημερομηνία:” in Greek)
• %l → archive label
• %m → mailto address
• %n → author display name (plain text, no markup)
• %N → author name + email as linked HTML
• %p → program name
• %s → subject (HTML-escaped, with stripsubject applied)
• %S → subject <meta name="Subject"> tag (message pages only)
• %A → author <meta name="Author"> tag (message pages only)
• %t → relative path to top-level index
• %u → expanded version link <a href=...>progname version</a>
• %v → version string
• %w → localized “Generated by” text
• %y → localized “Author:” label