@Comment{
  @Book{tes03,
    author =	 {John Smith},
    title =	 {Cooking},
    publisher =	 {Culinary Expert},
    year =	 1890
  }
}

@String(mar = "march")

@Book{sweig-42,
  Author =	 { Stefan Sweig },
  title =	 { The impossible book },
  publisher =	 { Dead Poet Society},
  year =	 1942,
  month =        mar
}

@String {firstname = "John"}
@String {lastname  = "Smith"}
@String {email      = firstname # "." # lastname # "@imag.en"}

@Article{key01,
  title = { The history of @ sign }
}

Everything " " outside {entries} is treated as comment in BibTeX.

@Article{key03,
  title = "A {bunch {of} braces {in}} title"
}

@preamble {"This bibliography was generated on \today"}