Fixed documentation for columns

replaced "overlay specifications" with "action specification", see #560 (comment)

doc/beamerug-localstructure.tex

@@ -941,8 +941,8 @@ \subsection{Splitting a Frame into Multiple Columns}
 
 The main environment for creating columns is called |columns|. Inside this environment, you can either place several |column| environments, each of which creates a new column, or use the |\column| command to create new columns.
 
-\begin{environment}{{columns}\sarg{overlay specification}\oarg{options}}
-  A multi-column area. If \meta{overlay specification} is present, the environment will only be shown on the specified slides. Inside the environment you should place only |column| environments or |\column| commands (see below). The following \meta{options} may be given:
+\begin{environment}{{columns}\sarg{action specification}\oarg{options}}
+  A multi-column area. If the \meta{action specification} is present, the given actions are taken on the specified slides, see Section~\ref{section-action-specifications}. Inside the environment you should place only |column| environments or |\column| commands (see below). The following \meta{options} may be given:
   \begin{itemize}
   \item
     \declare{|b|} will cause the bottom lines of the columns to be vertically aligned.
@@ -991,8 +991,8 @@ \subsection{Splitting a Frame into Multiple Columns}
 
 To create a column, you can either use the |column| environment or the |\column| command.
 
-\begin{environment}{{column}\sarg{overlay specification}\oarg{placement}\marg{column width}}
-  Creates a single column of width \meta{column width}. If \meta{overlay specification} is present, the column will only be shown on the specified slides. The vertical placement of the enclosing |columns| environment can be overruled by specifying a specific \meta{placement} (|t| and |T| for the two top modes, |c| for centered, and |b| for bottom).
+\begin{environment}{{column}\sarg{action specification}\oarg{placement}\marg{column width}}
+  Creates a single column of width \meta{column width}. If the \meta{action specification} is present, the given actions are taken on the specified slides, see Section~\ref{section-action-specifications}. The vertical placement of the enclosing |columns| environment can be overruled by specifying a specific \meta{placement} (|t| and |T| for the two top modes, |c| for centered, and |b| for bottom).
 
   \example
   The following code has the same effect as the above examples:
@@ -1012,7 +1012,7 @@ \subsection{Splitting a Frame into Multiple Columns}
 
 \end{environment}
 
-\begin{command}{{\column}\sarg{overlay specification}\oarg{placement}\marg{column width}}
+\begin{command}{{\column}\sarg{action specification}\oarg{placement}\marg{column width}}
   Starts a single column. The parameters and options are the same as for the |column| environment. The column automatically ends with the next occurrence of |\column| or of a |column| environment or of the end of the current |columns| environment.
 
   \example