Obtener los saltos de página correctos para una macro \beginsection

Question

Encontré este código en la pregunta.Sin sangría en el primer párrafo de una sección en Plain TeX

\def\mysection#1{%
  \goodbreak
  \vskip2\baselineskip
  \noindent #1\par
  \nobreak
  \vskip\baselineskip
  \everypar={{\setbox0\lastbox}\everypar={}}}

pero no estira la parte inferior de la página cuando la página se divide en un nuevo párrafo (aquí el estiramiento se encontró en los saltos alrededor del título de la sección).

Así que lo intenté

\def\mysection#1{%
  \filbreak
  \vskip2\baselineskip
  \noindent #1\par
  \nobreak
  \vskip\baselineskip
  \everypar={{\setbox0\lastbox}\everypar={}}}

lo que ahora fomenta demasiado los saltos de página... (La segunda página se rompió antes de la sección 3d)

Aquí está mi pregunta: ¿cómo puedo definir \mysectioneso?

• divide la página si (y sólo si) no hay espacio para el título de la sección y la primera línea del primer párrafo de la sección;
• ¿Termina la página con un \hfilsi la página está dividida en el título de una sección?

Archivo de prueba:

\def\mysection#1{%
    \filbreak
    %\goodbreak
    \vskip2\baselineskip
    \noindent #1\par
    \nobreak
    \vskip\baselineskip
    \everypar={{\setbox0\lastbox}\everypar={}}}

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

\mysection{Hello world!}
some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

\mysection{Nice title!}
some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

\mysection{This one too}
some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 
\bye

Answer 1

Utilice la misma idea que \filbreak, pero con un pluscomponente finito:

\def\mysection#1{%
    \par
    \vskip2\baselineskip plus 3\baselineskip
    \penalty-500
    \vskip 0pt plus -3\baselineskip
    \noindent #1\par
    \nobreak
    \vskip\baselineskip
    \everypar={{\setbox0\lastbox}\everypar={}}}

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

\mysection{Hello world!}
some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

\mysection{Nice title!}
some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

\mysection{This one too}
some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text some text 

\bye

¿Cuál es la idea de \filbreak? El comando emite dos \vskipcomandos con un \penaltypunto intermedio:

\vskip<specs-a>
\penalty<amount>
\vskip<specs-b>

Hay tres casos:

1. No se toman saltos de página en esos elementos.

2. Se toma un salto de página en el primer pegamento.

3. Se toma un salto de página en la pena.

Observe que el segundo pegamento no es un punto de salto de página factible, porque está precedido por una penalización, que es un elemento descartable.

En el caso 1 aparecerán los dos pegamentos en la página; en el caso 2, los tres elementos desaparecerán en el salto de página; en el caso 3, el segundo elemento de pegamento desaparecerá.

Ahora bien, ¿qué \filbreakhace? Su definición es

\par\vfil\penalty-200\vfilneg

donde \vfily \vfilnegson primitivas equivalentes a

\vskip 0pt plus 1fil

y

\vskip 0pt plus -1fil

respectivamente. Entonces, en el caso 1, no resultará ningún espacio vertical, porque los infinitos componentes se cancelan entre sí. En el caso 2, no se “verá nada”. En el caso 3, solo plus 1filactuará el, agregando una capacidad de estiramiento infinita a la página.

En mi variación utilizo la misma penalización que \goodbreak(-500), pero el primer elemento de pegamento es 2\baselineskip plus 3\baselineskipy el segundo elemento de pegamento es 0pt plus -3\baselineskip. La idea es la misma: en el caso 1 la cantidad neta de pegamento es 2\baselineskip; en el caso 2 no se ve nada; en el caso 3, la cantidad de estiramiento es 3\baselineskip, por lo que se invitará a TeX a no dejar más espacio del necesario para acomodar tres líneas: el título de la sección, la línea vacía después y la primera línea del siguiente párrafo. Para ser honesto, lo intentaría con dos líneas para evitar una línea de club.