Messages have different levels of priority that determine which selector will be executed first in an expression. This means the left most selector will be executed first, followed by the next left-most, etc. However, this rule does not apply given selectors with different priority levels. If the expression contains different priority selectors the order of evaluation is from highest to lowest priority. Priority can be changed by using parentheses.
Parentheses have the highest priority.
A Block expression in smalltalk represents a deferred sequence of messages . Blocks are used to implement control structures.