You can use the Format menu and pick Cells and then choose the text format. Another thing you can do is to type a single quote in first and then the number, and it will be treated as text, like this:
'100
Format the cell as text. You also can input a formula: =text(A1) Remark: if the content is in cell A1.
Rotating Text
The numbers are stored as text in Excel (that_¾_s why you see this green part in the left upper corner). When you convert the text to numbers, you can get an even stranger number: 578.510.000.
It converts numbers to Thai text. So if you wanted the number 6 in Thai, you can do something like this: =BAHTTEXT(6) It does not convert actual text and it does not convert numbers to English text.
alpha
Convert it to text.
apostrophe
There is no reason why you cannot type that in. As there are letters in it, it will be treated by Excel as text.
In effect a cell in Excel is a box where either text, number or formula can be placed.
In Excel it is between -90 deg and +90 deg.
The origin of the sheet usually doesn't matter. You can apply bold styles to PHP generated sheets as you would in any other sheet: right click the cell or text you want to make bold, and select the appropriate option to change font styles (which varies depending on your version of Microsoft Excel).
number instead of a letter (text)