When using 'Contains' in Linq query:

```
var camlQuery = new CamlQuery();
var listItems = list.GetItems(camlQuery);

var itemQuery = listItems.Where(i => i.FieldValuesAsText["Title"].Contains("van")).Include(
    item => item["ID"],
    item => item["Title"]);

var itemsFound = clientContext.LoadQuery(itemQuery);
clientContext.ExecuteQuery();

```

I get an error like: "The 'Contains' member cannot be used in the expression."

But when using a CamlQuery like:

```
var camlQuery = new CamlQuery();
camlQuery.ViewXml = @"
    <View>
        <ViewFields>
            <FieldRef Name='ID'/>
            <FieldRef Name='Title'/>
        </ViewFields>
        <Query>
            <Where>
                <Contains>
                    <FieldRef Name='Title' />
                    <Value Type='Text'>van</Value>
                </Contains>
            </Where>
        </Query>
        <RowLimit>10</RowLimit>
    </View>";

clientContext.Load(listItems);
clientContext.ExecuteQuery();

```

It works fine.

What is the explanation for this?