No início do arquivo fonte beamerbasedecode.styda beamerclasse, duas opções são definidas:
\newif\ifbeamer@anotherslide
\newif\ifbeamer@localanotherslide
Ao ler beamerbasedecode.stye beamerbaseframe.sty, tenho algum conhecimento sobre \ifbeamer@anotherslide: Em todos frameos ambientes, beamerchama \beamer@masterdecodee \beamer@masterdecodemudaria o switch \ifbeamer@anotherslide. Embora seja verdade, beamerele chama \beamer@masterdecoderepetidamente e, por fim, gera todos os slides do quadro.
Por dentro \beamerbasedecode.sty, parece que \ifbeamer@anotherslidee \ifbeamer@localanotherslidesempre têm o mesmo valor:
\global\beamer@anotherslidetrue\beamer@localanotherslidetrue
A única diferença é o \globalanterior ao primeiro. Mas na macro principal \beamer@masterdecode, a segunda também se torna global.
\def\beamer@stoptexts{| stop:0| }
{
\catcode`\|=13
\catcode`\:=13
\catcode`\,=13
\catcode`\.=13
\catcode`\+=13
\catcode`\-=13
\catcode`\(=13
\catcode`\)=13
\catcode`\ =13
\gdef\beamer@masterdecode#1{% must be called within a group
\ifnum\catcode`\|=13\edef|{\string|}\fi%
\ifnum\catcode`\:=13\edef:{\string:}\fi%
\ifnum\catcode`\,=13\edef,{\string,}\fi%
\ifnum\catcode`\.=13\edef.{\string.}\fi%
\ifnum\catcode`\+=13\edef+{\string+}\fi%
\ifnum\catcode`\-=13\edef-{\string-}\fi%
\ifnum\catcode`\(=13\edef({\string(}\fi%
\ifnum\catcode`\)=13\edef){\string)}\fi%
\ifnum\catcode`\ =13\edef {\string }\fi%
\edef\beamer@@@temp{#1\beamer@stoptexts}%
\beamer@localanotherslidefalse%
\setbox0=\hbox{%
\expandafter\beamer@decode\beamer@@@temp%
\ifbeamer@localanotherslide\global\beamer@localanotherslidetrue\fi}%
}%
Isso me confunde: quais são as diferenças entre \ifbeamer@anotherslidee \ifbeamer@localanotherslide? Por que precisamos \ifbeamer@localanotherslide?