fix: minor rewording of cast.md for clarity (#137)

Author: gregfenton

src/md/parse/options/cast.md

@@ -7,28 +7,29 @@ keywords: ['csv', 'parse', 'options', 'cast', 'context', 'lines', 'quoting']
 
 # Option `cast`
 
-The `cast` option alter a value. It works at the field level of a record. It is possible to transform its value or change its type.
+The `cast` option works at the field-level to alter its value. It is possible to transform the field's value or change its type.
 
 * Type: `function`
 * Optional
 * Default: `undefined`
 * Since: 2.2.0
 * Related: `cast_date`, [`info`](/parse/options/info/), [`on_record`](/parse/options/on_record/) — see [Available Options](/parse/options/#available-options)
 
-Its value is expected to be a function which receives a context rich of information. It gives full control over a field. The [`test/option.cast.coffee`](https://github.com/adaltas/node-csv/blob/master/packages/csv-parse/test/option.cast.coffee) test provides insights on how to use it and its supported functionalities.
+The `cast` value is expected to be a function that receives context-rich information. The function has full control over a field. The [`test/option.cast.coffee`](https://github.com/adaltas/node-csv/blob/master/packages/csv-parse/test/option.cast.coffee) test provides insights on how to use it and its supported functionalities.
 
 ## Context
 
-The function is called with 2 arguments: the field value and a context object. The context object expose the following properties:
+The `cast` function is called with 2 arguments: the field `value` and the `context` object.
 
+The `context` object exposes the following properties:
 * `column` (number|string)   
-  The column name if the `columns` options is defined or the field position.
+  The column name if the `columns` options is defined, or the field position.
 * `empty_lines` (number)   
   Internal counter of empty lines encountered until this field.
 * `header` (boolean)   
   A boolean indicating if the provided value is a part of the header.
 * `index` (number)   
-  The field position starting at 0.
+  The field position within the current record starting at 0.
 * `invalid_field_length` (number)   
   Number of records with a non uniform length when [`relax_column_count`](/parse/options/relax_column_count/) is true. It was named `skipped_lines` until version 3.
 * `lines` (number)   
@@ -38,15 +39,15 @@ The function is called with 2 arguments: the field value and a context object. T
 * `records` (number)   
   The number of records which have been fully parsed. It was named `count` until version 3.
 
-The [cast example](https://github.com/adaltas/node-csv/blob/master/packages/csv-parse/samples/option.cast.js) uses the context to transform the first filed into a date and replace the second field with the injected context:
+The [cast example](https://github.com/adaltas/node-csv/blob/master/packages/csv-parse/samples/option.cast.js) uses the context to transform the first field into a date and replace the second field with the injected context:
 
 `embed:packages/csv-parse/samples/option.cast.js`
 
 ## Using the `cast` and `columns` functions conjointly
 
-The `cast` function is called field by field, whether it is considered a header or not. The `columns` function is called once the first record is created (if treated as a header). For this reason, `cast` is executed before `columns`.
+The `cast` function is called for each and every field, whether it is considered a header or not. The `columns` function is called once the first record is created (if treated as a header). For this reason, `cast` is executed before `columns`.
 
-To distinguish a header field from a data field in the `cast` function, use the [`context.header` property](https://github.com/adaltas/node-csv/blob/master/packages/csv-parse/samples/option.cast.header.column.fn.js) in the second argument of the `cast` function:
+To distinguish a header field from a data field in the `cast` function, use the [`context.header` property](https://github.com/adaltas/node-csv/blob/master/packages/csv-parse/samples/option.cast.header.column.fn.js) from the second argument to the `cast` function:
 
 `embed:packages/csv-parse/samples/option.cast.header.column.fn.js`