<\body> As a general rule, the behaviour of most structured editing operations is conditioned by the >. By default, the innermost tag which contains the cursor. Whenever some selection is active, the current focus is the innermost tag which contains the selection. During structured operations, such as navigating among similar tags, the current focus may temporarily be set to something else. The current focus is visually indicated by the innermost cyan box around the cursor. For instance, the commands , , and have a particular meaning both inside tables and trees. Inside tables, they allow you to insert new rows and columns (see figure). Inside trees, they correspond to the insertion of new nodes (see figure). Whenever you inside a tree inside a table, then the innermost tag is a tree, and node insertions will take precedence over the insertion of new rows and columns. In many cases, a ``default particular behaviour'' has been defined for all tags minus some exceptional ones. In our example of structured insertion, the default behaviour of and is to insert a new argument to the tag at the left or at the right (when allowed). <\big-figure> <\equation*> |>|>|||>>>>||>|>||||>>>>|>||>||||>>>>||>||>|>|||>>>>|>|>|||>|||>>>> <|big-figure> Assume that the cursor is at the position of inside the left-most matrix. Then the four other matrices respectively correspond to the insertion of a new column at the left() or right(), a new row above() or below(). <\big-figure||d>|c|d>|d>|c>|d>>|d>> Assume that the cursor is at the position of inside the left-most tree. Then the four other trees respectively correspond to the insertion of a new node at the left(), at the right(), above() or below(). Similarly, in the case of matrices, the keys , , and can be used for inserting a new first or last column, a new first or last row. The keys and are mapped to the commands for backward forward . In the case of matrices, this will result in the removal of the column before or after the cursor (see figure). In order to remove the enclosing environment you may use or . <\big-figure> <\equation*> |>|>|||>>>>>|>||>>>>|c>>||>>>>b <|big-figure> Assume that the cursor is at the position of inside the left-most matrix. Then pressing the keys and respectively result in the next two matrices. Pressing either or replaces the matrix by the content of the cell in which you are, leaving you with the at the right-hand side. <\initial> <\collection>