This site requires a browser – like Firefox – which supports MathML.

Firemath - The MathML Editor

Example: mtables

<mtable>s are the MathML presentation elements with the largest number of attributes. Firefox supports a sub-set of these. You should keep this fact in mind when doing experiments with mtable attributes.
Start with inserting 'det' as an operator followed by fences . When the cursor is within the fences, click onto the mtable button , set the number of rows and columns to four, choose a conventional table type and click OK. Place an 'a' as identifier on each of the main diagonal positions to obtain

det a a a a

Place the cursor such that it covers the entire mtable (without the fences) and click onto the attributes button . Select the tab labeled 'Rows' of the opened popup window. Notice that the corresponding panel has four tabs labeled 'Row 1' through 'Row 4'. Now, for row 1, column 3, set 'Row align' to 'center', 'Rowspan' to '2', and 'Columnspan' to '2'. Similar, for row 3, column 1, set 'Row align' to 'center', 'Rowspan' to '2', and 'Columnspan' to '2'. Insert '0' twice at the desired positions. Locate the cursor on one of the just inserted 0s and click the attributes button . Right behind 'Mathsize' select the second radio button, insert 1.5 and select 'em'. Repeat this procedure with the other '0', such that you get

det a 0 a 0 a a

Move the cursor to the very right and insert an '=' operator. Click onto the fences button and insert another mtable with two rows and two columns within the fences. Place the cursor over the fences and click the attributes button . Remove the entry right of 'Close' and click OK. Place the cursor over the mtable and click the attributes button. On the panel with the 'Table' tab set attribute 'Column-align' to 'left'. Now you are ready to fill in the four entries of our mtable such that you receive

det a 0 a 0 a a = 0 , if a = 0 a 4 , else

For the latter, you should use 'Text' entries for the commas in the first column and for the words 'if' and 'else' in the second one. Use an <mspace> between the 'if' and the a .